Internet DRAFT - draft-ietf-gnap-core-protocol
draft-ietf-gnap-core-protocol
GNAP J. Richer, Ed.
Internet-Draft Bespoke Engineering
Intended status: Standards Track F. Imbault
Expires: 13 August 2024 acert.io
10 February 2024
Grant Negotiation and Authorization Protocol
draft-ietf-gnap-core-protocol-18
Abstract
GNAP defines a mechanism for delegating authorization to a piece of
software, and conveying the results and artifacts of that delegation
to the software. This delegation can include access to a set of APIs
as well as subject information passed directly to the software.
Status of This Memo
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This Internet-Draft will expire on 13 August 2024.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
1.2. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3. Elements . . . . . . . . . . . . . . . . . . . . . . . . 10
1.4. Trust relationships . . . . . . . . . . . . . . . . . . . 11
1.5. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . 13
1.6. Sequences . . . . . . . . . . . . . . . . . . . . . . . . 16
1.6.1. Overall Protocol Sequence . . . . . . . . . . . . . . 16
1.6.2. Redirect-based Interaction . . . . . . . . . . . . . 19
1.6.3. User-code Interaction . . . . . . . . . . . . . . . . 22
1.6.4. Asynchronous Authorization . . . . . . . . . . . . . 25
1.6.5. Software-only Authorization . . . . . . . . . . . . . 27
1.6.6. Refreshing an Expired Access Token . . . . . . . . . 28
1.6.7. Requesting Subject Information Only . . . . . . . . . 30
1.6.8. Cross-User Authentication . . . . . . . . . . . . . . 31
2. Requesting Access . . . . . . . . . . . . . . . . . . . . . . 34
2.1. Requesting Access to Resources . . . . . . . . . . . . . 36
2.1.1. Requesting a Single Access Token . . . . . . . . . . 36
2.1.2. Requesting Multiple Access Tokens . . . . . . . . . . 39
2.2. Requesting Subject Information . . . . . . . . . . . . . 41
2.3. Identifying the Client Instance . . . . . . . . . . . . . 42
2.3.1. Identifying the Client Instance by Reference . . . . 44
2.3.2. Providing Displayable Client Instance Information . . 45
2.3.3. Authenticating the Client Instance . . . . . . . . . 46
2.4. Identifying the User . . . . . . . . . . . . . . . . . . 46
2.4.1. Identifying the User by Reference . . . . . . . . . . 48
2.5. Interacting with the User . . . . . . . . . . . . . . . . 48
2.5.1. Start Mode Definitions . . . . . . . . . . . . . . . 50
2.5.2. Interaction Finish Methods . . . . . . . . . . . . . 53
2.5.3. Hints . . . . . . . . . . . . . . . . . . . . . . . . 55
3. Grant Response . . . . . . . . . . . . . . . . . . . . . . . 56
3.1. Request Continuation . . . . . . . . . . . . . . . . . . 58
3.2. Access Tokens . . . . . . . . . . . . . . . . . . . . . . 59
3.2.1. Single Access Token . . . . . . . . . . . . . . . . . 59
3.2.2. Multiple Access Tokens . . . . . . . . . . . . . . . 63
3.3. Interaction Modes . . . . . . . . . . . . . . . . . . . . 64
3.3.1. Redirection to an arbitrary URI . . . . . . . . . . . 66
3.3.2. Launch of an application URI . . . . . . . . . . . . 66
3.3.3. Display of a Short User Code . . . . . . . . . . . . 67
3.3.4. Display of a Short User Code and URI . . . . . . . . 68
3.3.5. Interaction Finish . . . . . . . . . . . . . . . . . 69
3.4. Returning Subject Information . . . . . . . . . . . . . . 69
3.5. Returning a Dynamically-bound Client Instance
Identifier . . . . . . . . . . . . . . . . . . . . . . . 71
3.6. Error Response . . . . . . . . . . . . . . . . . . . . . 72
4. Determining Authorization and Consent . . . . . . . . . . . . 74
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4.1. Starting Interaction With the End User . . . . . . . . . 78
4.1.1. Interaction at a Redirected URI . . . . . . . . . . . 79
4.1.2. Interaction at the Static User Code URI . . . . . . . 80
4.1.3. Interaction at a Dynamic User Code URI . . . . . . . 81
4.1.4. Interaction through an Application URI . . . . . . . 82
4.2. Post-Interaction Completion . . . . . . . . . . . . . . . 83
4.2.1. Completing Interaction with a Browser Redirect to the
Callback URI . . . . . . . . . . . . . . . . . . . . 84
4.2.2. Completing Interaction with a Direct HTTP Request
Callback . . . . . . . . . . . . . . . . . . . . . . 85
4.2.3. Calculating the interaction hash . . . . . . . . . . 85
5. Continuing a Grant Request . . . . . . . . . . . . . . . . . 87
5.1. Continuing After a Completed Interaction . . . . . . . . 89
5.2. Continuing During Pending Interaction (Polling) . . . . . 91
5.3. Modifying an Existing Request . . . . . . . . . . . . . . 93
5.4. Revoking a Grant Request . . . . . . . . . . . . . . . . 100
6. Token Management . . . . . . . . . . . . . . . . . . . . . . 100
6.1. Rotating the Access Token Value . . . . . . . . . . . . . 101
6.1.1. Binding a New Key to the Rotated Access Token . . . . 103
6.2. Revoking the Access Token . . . . . . . . . . . . . . . . 104
7. Securing Requests from the Client Instance . . . . . . . . . 105
7.1. Key Formats . . . . . . . . . . . . . . . . . . . . . . . 106
7.1.1. Key References . . . . . . . . . . . . . . . . . . . 107
7.1.2. Key Protection . . . . . . . . . . . . . . . . . . . 108
7.2. Presenting Access Tokens . . . . . . . . . . . . . . . . 108
7.3. Proving Possession of a Key with a Request . . . . . . . 109
7.3.1. HTTP Message Signatures . . . . . . . . . . . . . . . 113
7.3.2. Mutual TLS . . . . . . . . . . . . . . . . . . . . . 120
7.3.3. Detached JWS . . . . . . . . . . . . . . . . . . . . 123
7.3.4. Attached JWS . . . . . . . . . . . . . . . . . . . . 127
8. Resource Access Rights . . . . . . . . . . . . . . . . . . . 132
8.1. Requesting Resources By Reference . . . . . . . . . . . . 136
9. Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . 139
9.1. RS-first Method of AS Discovery . . . . . . . . . . . . . 140
9.2. Dynamic grant endpoint discovery . . . . . . . . . . . . 142
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 143
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 143
11.1. HTTP Authentication Scheme Registration . . . . . . . . 144
11.2. GNAP Grant Request Parameters . . . . . . . . . . . . . 144
11.2.1. Registration Template . . . . . . . . . . . . . . . 144
11.2.2. Initial Contents . . . . . . . . . . . . . . . . . . 145
11.3. GNAP Access Token Flags . . . . . . . . . . . . . . . . 145
11.3.1. Registration Template . . . . . . . . . . . . . . . 145
11.3.2. Initial Contents . . . . . . . . . . . . . . . . . . 146
11.4. GNAP Subject Information Request Fields . . . . . . . . 146
11.4.1. Registration Template . . . . . . . . . . . . . . . 146
11.4.2. Initial Contents . . . . . . . . . . . . . . . . . . 147
11.5. GNAP Assertion Formats . . . . . . . . . . . . . . . . . 147
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11.5.1. Registration Template . . . . . . . . . . . . . . . 147
11.5.2. Initial Contents . . . . . . . . . . . . . . . . . . 147
11.6. GNAP Client Instance Fields . . . . . . . . . . . . . . 148
11.6.1. Registration Template . . . . . . . . . . . . . . . 148
11.6.2. Initial Contents . . . . . . . . . . . . . . . . . . 148
11.7. GNAP Client Instance Display Fields . . . . . . . . . . 149
11.7.1. Registration Template . . . . . . . . . . . . . . . 149
11.7.2. Initial Contents . . . . . . . . . . . . . . . . . . 149
11.8. GNAP Interaction Start Modes . . . . . . . . . . . . . . 150
11.8.1. Registration Template . . . . . . . . . . . . . . . 150
11.8.2. Initial Contents . . . . . . . . . . . . . . . . . . 151
11.9. GNAP Interaction Finish Methods . . . . . . . . . . . . 151
11.9.1. Registration Template . . . . . . . . . . . . . . . 151
11.9.2. Initial Contents . . . . . . . . . . . . . . . . . . 152
11.10. GNAP Interaction Hints . . . . . . . . . . . . . . . . . 152
11.10.1. Registration Template . . . . . . . . . . . . . . . 152
11.10.2. Initial Contents . . . . . . . . . . . . . . . . . 152
11.11. GNAP Grant Response Parameters . . . . . . . . . . . . . 153
11.11.1. Registration Template . . . . . . . . . . . . . . . 153
11.11.2. Initial Contents . . . . . . . . . . . . . . . . . 153
11.12. GNAP Interaction Mode Responses . . . . . . . . . . . . 154
11.12.1. Registration Template . . . . . . . . . . . . . . . 154
11.12.2. Initial Contents . . . . . . . . . . . . . . . . . 154
11.13. GNAP Subject Information Response Fields . . . . . . . . 155
11.13.1. Registration Template . . . . . . . . . . . . . . . 155
11.13.2. Initial Contents . . . . . . . . . . . . . . . . . 155
11.14. GNAP Error Codes . . . . . . . . . . . . . . . . . . . . 156
11.14.1. Registration Template . . . . . . . . . . . . . . . 156
11.14.2. Initial Contents . . . . . . . . . . . . . . . . . 156
11.15. GNAP Key Proofing Methods . . . . . . . . . . . . . . . 157
11.15.1. Registration Template . . . . . . . . . . . . . . . 157
11.15.2. Initial Contents . . . . . . . . . . . . . . . . . 158
11.16. GNAP Key Formats . . . . . . . . . . . . . . . . . . . . 158
11.16.1. Registration Template . . . . . . . . . . . . . . . 158
11.16.2. Initial Contents . . . . . . . . . . . . . . . . . 159
11.17. GNAP Authorization Server Discovery Fields . . . . . . . 159
11.17.1. Registration Template . . . . . . . . . . . . . . . 159
11.17.2. Initial Contents . . . . . . . . . . . . . . . . . 160
12. Implementation Status . . . . . . . . . . . . . . . . . . . . 160
13. Security Considerations . . . . . . . . . . . . . . . . . . . 161
13.1. TLS Protection in Transit . . . . . . . . . . . . . . . 161
13.2. Signing Requests from the Client Software . . . . . . . 162
13.3. MTLS Message Integrity . . . . . . . . . . . . . . . . . 164
13.4. MTLS Deployment Patterns . . . . . . . . . . . . . . . . 164
13.5. Protection of Client Instance Key Material . . . . . . . 165
13.6. Protection of Authorization Server . . . . . . . . . . . 166
13.7. Symmetric and Asymmetric Client Instance Keys . . . . . 167
13.8. Generation of Access Tokens . . . . . . . . . . . . . . 168
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13.9. Bearer Access Tokens . . . . . . . . . . . . . . . . . . 169
13.10. Key-Bound Access Tokens . . . . . . . . . . . . . . . . 170
13.11. Exposure of End-user Credentials to Client Instance . . 171
13.12. Mixing Up Authorization Servers . . . . . . . . . . . . 172
13.13. Processing of Client-Presented User Information . . . . 172
13.14. Client Instance Pre-registration . . . . . . . . . . . . 173
13.15. Client Instance Impersonation . . . . . . . . . . . . . 175
13.16. Client-Hosted Logo URI . . . . . . . . . . . . . . . . . 175
13.17. Interception of Information in the Browser . . . . . . . 176
13.18. Callback URI Manipulation . . . . . . . . . . . . . . . 176
13.19. Redirection Status Codes . . . . . . . . . . . . . . . . 177
13.20. Interception of Responses from the AS . . . . . . . . . 178
13.21. Key Distribution . . . . . . . . . . . . . . . . . . . . 178
13.22. Key Rotation Policy . . . . . . . . . . . . . . . . . . 179
13.23. Interaction Finish Modes and Polling . . . . . . . . . . 180
13.24. Session Management for Interaction Finish Methods . . . 180
13.25. Calculating Interaction Hash . . . . . . . . . . . . . . 182
13.26. Storage of Information During Interaction and
Continuation . . . . . . . . . . . . . . . . . . . . . 184
13.27. Denial of Service (DoS) through Grant Continuation . . . 185
13.28. Exhaustion of Random Value Space . . . . . . . . . . . . 186
13.29. Front-channel URIs . . . . . . . . . . . . . . . . . . . 186
13.30. Processing Assertions . . . . . . . . . . . . . . . . . 187
13.31. Stolen Token Replay . . . . . . . . . . . . . . . . . . 188
13.32. Self-contained Stateless Access Tokens . . . . . . . . . 189
13.33. Network Problems and Token and Grant Management . . . . 190
13.34. Server-side Request Forgery (SSRF) . . . . . . . . . . . 191
13.35. Multiple Key Formats . . . . . . . . . . . . . . . . . . 192
13.36. Asynchronous Interactions . . . . . . . . . . . . . . . 193
13.37. Compromised RS . . . . . . . . . . . . . . . . . . . . . 194
13.38. AS-Provided Token Keys . . . . . . . . . . . . . . . . . 194
14. Privacy Considerations . . . . . . . . . . . . . . . . . . . 195
14.1. Surveillance . . . . . . . . . . . . . . . . . . . . . . 195
14.1.1. Surveillance by the Client . . . . . . . . . . . . . 195
14.1.2. Surveillance by the Authorization Server . . . . . . 196
14.2. Stored Data . . . . . . . . . . . . . . . . . . . . . . 196
14.3. Intrusion . . . . . . . . . . . . . . . . . . . . . . . 197
14.4. Correlation . . . . . . . . . . . . . . . . . . . . . . 197
14.4.1. Correlation by Clients . . . . . . . . . . . . . . . 197
14.4.2. Correlation by Resource Servers . . . . . . . . . . 198
14.4.3. Correlation by Authorization Servers . . . . . . . . 199
14.5. Disclosure in Shared References . . . . . . . . . . . . 199
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 199
15.1. Normative References . . . . . . . . . . . . . . . . . . 199
15.2. Informative References . . . . . . . . . . . . . . . . . 202
Appendix A. Document History . . . . . . . . . . . . . . . . . . 204
Appendix B. Compared to OAuth 2.0 . . . . . . . . . . . . . . . 209
Appendix C. Example Protocol Flows . . . . . . . . . . . . . . . 212
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C.1. Redirect-Based User Interaction . . . . . . . . . . . . . 212
C.2. Secondary Device Interaction . . . . . . . . . . . . . . 216
C.3. No User Involvement . . . . . . . . . . . . . . . . . . . 219
C.4. Asynchronous Authorization . . . . . . . . . . . . . . . 220
C.5. Applying OAuth 2.0 Scopes and Client IDs . . . . . . . . 224
Appendix D. Interoperability Profiles . . . . . . . . . . . . . 225
D.1. Web-based Redirection . . . . . . . . . . . . . . . . . . 226
D.2. Secondary Device . . . . . . . . . . . . . . . . . . . . 226
Appendix E. Guidance for Extensions . . . . . . . . . . . . . . 227
Appendix F. JSON Structures and Polymorphism . . . . . . . . . . 228
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 229
1. Introduction
This protocol allows a piece of software, the client instance, to
request delegated authorization to resource servers and subject
information. The delegated access to the resource server can be used
by the client instance to access resources and APIs on behalf a
resource owner, and delegated access to subject information can in
turn be used by the client instance to make authentication decisions.
This delegation is facilitated by an authorization server usually on
behalf of a resource owner. The end user operating the software can
interact with the authorization server to authenticate, provide
consent, and authorize the request as a resource owner.
The process by which the delegation happens is known as a grant, and
GNAP allows for the negotiation of the grant process over time by
multiple parties acting in distinct roles.
This specification focuses on the portions of the delegation process
facing the client instance. In particular, this specification
defines interoperable methods for a client instance to request,
negotiate, and receive access to information facilitated by the
authorization server. This specification additionally defines
methods for the client instance to access protected resources at a
resource server. This specification also discusses discovery
mechanisms for the client instance to configure itself dynamically.
The means for an authorization server and resource server to
interoperate are discussed in the companion document,
[I-D.ietf-gnap-resource-servers].
The focus of this protocol is to provide interoperability between the
different parties acting in each role, and is not to specify
implementation details of each. Where appropriate, GNAP may make
recommendations about internal implementation details, but these
recommendations are to ensure the security of the overall deployment
rather than to be prescriptive in the implementation.
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This protocol solves many of the same use cases as OAuth 2.0
[RFC6749], OpenID Connect [OIDC], and the family of protocols that
have grown up around that ecosystem. However, GNAP is not an
extension of OAuth 2.0 and is not intended to be directly compatible
with OAuth 2.0. GNAP seeks to provide functionality and solve use
cases that OAuth 2.0 cannot easily or cleanly address. Appendix B
further details the protocol rationale compared to OAuth 2.0. GNAP
and OAuth 2.0 will likely exist in parallel for many deployments, and
considerations have been taken to facilitate the mapping and
transition from existing OAuth 2.0 systems to GNAP. Some examples of
these can be found in Appendix C.5.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document contains non-normative examples of partial and complete
HTTP messages, JSON structures, URIs, query components, keys, and
other elements. Whenever possible, the document uses URI as a
generic term, since it aligns with [RFC3986] recommendations and
matches better with the intent that the identifier may be reachable
through various/generic means (compared to URLs). Some examples use
a single trailing backslash \ to indicate line wrapping for long
values, as per [RFC8792]. The \ character and leading spaces on
wrapped lines are not part of the value.
This document uses the term "mutual TLS" as defined by [RFC8705].
The shortened form "MTLS" is used to mean the same thing.
For brevity, the term "signature" on its own is used in this document
to refer to both digital signatures (which use asymmetric
cryptography) and keyed MACs (which use symmetric cryptography).
Similarly, the verb "sign" refers to the generation of either a
digital signature or keyed MAC over a given signature base. The
qualified term "digital signature" refers specifically to the output
of an asymmetric cryptographic signing operation.
1.2. Roles
The parties in GNAP perform actions under different roles. Roles are
defined by the actions taken and the expectations leveraged on the
role by the overall protocol.
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+-------------+ +------------+
| | | |
|Authorization| | Resource |
| Server | | Server |
| |<--+ +--->| |
+-----+-------+ | | +------------+
║ | |
║ +--+---+---+
║ | Client |
║ | Instance |
║ +----+-----+
║ ║
.----+----. ║ .----------.
| | +=====+ |
| Resource | | End |
| Owner | ~ ~ ~ ~ ~ ~ | User |
| | | |
`---------` `----------`
Legend
===== indicates interaction between a human and computer
----- indicates interaction between two pieces of software
~ ~ ~ indicates a potential equivalence or out-of-band
communication between roles
Figure 1: Figure 1: Roles in GNAP
Authorization Server (AS): server that grants delegated privileges
to a particular instance of client software in the form of access
tokens or other information (such as subject information). The AS
is uniquely defined by the _grant endpoint URI_, which the
absolute URI where grant requests are started by clients.
Client: application that consumes resources from one or several RSs,
possibly requiring access privileges from one or several ASs. The
client is operated by the end user or it runs autonomously on
behalf of a resource owner.
Example: a client can be a mobile application, a web application,
a back-end data processor, etc.
Note: this specification differentiates between a specific
instance (the client instance, identified by its unique key) and
the software running the instance (the client software). For some
kinds of client software, there could be many instances of that
software, each instance with a different key.
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Resource Server (RS): server that provides an API on protected
resources, where operations on the API require a valid access
token issued by a trusted AS.
Resource Owner (RO): subject entity that may grant or deny
operations on resources it has authority upon.
Note: the act of granting or denying an operation may be manual
(i.e. through an interaction with a physical person) or automatic
(i.e. through predefined organizational rules).
End user: natural person that operates a client instance.
Note: that natural person may or may not be the same entity as the
RO.
The design of GNAP does not assume any one deployment architecture,
but instead attempts to define roles that can be fulfilled in a
number of different ways for different use cases. As long as a given
role fulfills all of its obligations and behaviors as defined by the
protocol, GNAP does not make additional requirements on its structure
or setup.
Multiple roles can be fulfilled by the same party, and a given party
can switch roles in different instances of the protocol. For
example, the RO and end user in many instances are the same person,
where a user is authorizing the client instance to act on their own
behalf at the RS. In this case, one party fulfills both of the RO
and end-user roles, but the roles themselves are still defined
separately from each other to allow for other use cases where they
are fulfilled by different parties.
For another example, in some complex scenarios, an RS receiving
requests from one client instance can act as a client instance for a
downstream secondary RS in order to fulfill the original request. In
this case, one piece of software is both an RS and a client instance
from different perspectives, and it fulfills these roles separately
as far as the overall protocol is concerned.
A single role need not be deployed as a monolithic service. For
example, a client instance could have front-end components that are
installed on the end user's device as well as a back-end system that
the front-end communicates with. If both of these components
participate in the delegation protocol, they are both considered part
of the client instance. If there are several copies of the client
software that run separately but all share the same key material,
such as a deployed cluster, then this cluster is considered a single
client instance. In these cases, the distinct components of what is
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considered a GNAP client instance may use any number of different
communication mechanisms between them, all of which would be
considered an implementation detail of the client instances and out
of scope of GNAP.
For another example, an AS could likewise be built out of many
constituent components in a distributed architecture. The component
that the client instance calls directly could be different from the
component that the RO interacts with to drive consent, since API
calls and user interaction have different security considerations in
many environments. Furthermore, the AS could need to collect
identity claims about the RO from one system that deals with user
attributes while generating access tokens at another system that
deals with security rights. From the perspective of GNAP, all of
these are pieces of the AS and together fulfill the role of the AS as
defined by the protocol. These pieces may have their own internal
communications mechanisms which are considered out of scope of GNAP.
1.3. Elements
In addition to the roles above, the protocol also involves several
elements that are acted upon by the roles throughout the process.
Access Token: a data artifact representing a set of rights and/or
attributes.
Note: an access token can be first issued to a client instance
(requiring authorization by the RO) and subsequently rotated.
Grant: (verb): to permit an instance of client software to receive
some attributes at a specific time and valid for a specific
duration and/or to exercise some set of delegated rights to access
a protected resource;
(noun): the act of granting permission to a client instance.
Privilege: right or attribute associated with a subject.
Note: the RO defines and maintains the rights and attributes
associated to the protected resource, and might temporarily
delegate some set of those privileges to an end user. This
process is refered to as privilege delegation.
Protected Resource: protected API (Application Programming
Interface) served by an RS and that can be accessed by a client,
if and only if a valid and sufficient access token is provided.
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Note: to avoid complex sentences, the specification document may
simply refer to "resource" instead of "protected resource".
Right: ability given to a subject to perform a given operation on a
resource under the control of an RS.
Subject: person or organization. The subject decides whether and
under which conditions its attributes can be disclosed to other
parties.
Subject Information: set of statements and attributes asserted by an
AS about a subject. These statements can be used by the client
instance as part of an authentication decision.
1.4. Trust relationships
GNAP defines its trust objective as: "the RO trusts the AS to ensure
access validation and delegation of protected resources to end users,
through third party clients."
This trust objective can be decomposed into trust relationships
between software elements and roles, especially the pairs end user/
RO, end user/client, client/AS, RS/RO, AS/RO, AS/RS. Trust of an
agent by its pair can exist if the pair is informed that the agent
has made a promise to follow the protocol in the past (e.g. pre-
registration, uncompromised cryptographic components) or if the pair
is able to infer by indirect means that the agent has made such a
promise (e.g. a compliant client request). Each agent defines its
own valuation function of promises given or received. Examples of
such valuations can be the benefits from interacting with other
agents (e.g. safety in client access, interoperability with identity
standards), the cost of following the protocol (including its
security and privacy requirements and recommendations), a ranking of
promise importance (e.g. a policy decision made by the AS), the
assessment of one's vulnerability or risk of not being able to defend
against threats, etc. Those valuations may depend on the context of
the request. For instance, the AS may decide to either take into
account or discard hints provided by the client, the RS may refuse
bearer tokens, etc. depending on the specific case in which GNAP is
used. Some promises can be conditional of some previous interactions
(e.g. repeated requests).
Looking back on each trust relationship:
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* end user/RO: this relationship exists only when the end user and
the RO are different, in which case the end user needs some out of
band mechanism of getting the RO consent (see Section 4). GNAP
generally assumes that humans can be authenticated thanks to
identity protocols (for instance, through an id_token assertion in
Section 2.2).
* end user/client: the client acts as a user agent. Depending on
the technology used (browser, SPA, mobile application, IoT device,
etc.), some interactions may or may not be possible (as described
in Section 2.5.1). Client developers implement requirements and
generally some recommendations or best practices, so that the end
users may confidently use their software. However, end users
might also be facing an attacker's client software or a poorly-
implemented client, without even realizing it.
* end user/AS: when the client supports the interaction feature (see
Section 3.3), the end user interacts with the AS through an AS-
provided interface. In may cases, this happens through a front-
channel interaction through the end user's browser. See
Section 13.29 for some considerations in trusting these
interactions.
* client/AS: An honest AS may be facing an attacker's client (as
discussed just above), or the reverse, and GNAP aims at making
common attacks impractical. The core specification makes access
tokens opaque to the client and defines the request/response
scheme in detail, therefore avoiding extra trust hypotheses from
this critical piece of software. Yet the AS may further define
cryptographic attestations or optional rules to simplify the
access of clients it already trusts, due to past behavior or
organizational policies (see Section 2.3).
* RS/RO: the RS promises it protects its resources on behalf of the
RO from unauthorized access, and only accepts valid access tokens
issued by a trusted AS. In case tokens are key bound, proper
validation of the proof method is expected from the RS.
* AS/RO: the AS is expected to follow the decisions made by the RO,
either through interactive consent requests, repeated
interactions, or automated rules (as described in Section 1.6).
Privacy considerations aim to reduce the risk of an honest but
too-curious AS, or the consequences of an unexpected user data
exposure.
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* AS/RS: the AS promises to issue valid access tokens to legitimate
client requests (i.e. after carrying out appropriate due
diligence, as defined in the GNAP protocol). Some optional
configurations are covered by [I-D.ietf-gnap-resource-servers].
A global assumption made by GNAP is that authorization requests are
security and privacy sensitive, and appropriate measures are
respectively detailed in Section 13 and Section 14.
A formal trust model is out of scope of this specification, but one
could be developed using techniques such as [promise-theory].
1.5. Protocol Flow
GNAP is fundamentally designed to allow delegated access to APIs and
other information, such as subject information, using a multi-stage,
stateful process. This process allows different parties to provide
information into the system to alter and augment the state of the
delegated access and its artifacts.
The underlying requested grant moves through several states as
different actions take place during the protocol:
.-----.
| |
+------+--+ | Continue
.---Need Interaction---->| | |
/ | Pending |<--`
/ .--Finish Interaction--+ |
/ / (approve/deny) +----+----+
/ / |
/ / | Cancel
/ v v
+-+----------+ +===========+
| | ║ ║
---Request-->| Processing +------Finalize---->║ Finalized ║
| | ║ ║
+-+----------+ +===========+
\ ^ ^
\ \ | Revoke or
\ \ | Finalize
\ \ +-----+----+
\ `-----Update---------+ |
\ | Approved |<--.
`-----No Interaction--->| | |
+-------+--+ | Continue
| |
`-----`
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Figure 2: Figure 2: State diagram of a grant request throughout GNAP
The state of the grant request is defined and managed by the AS,
though the client instance also needs to manage its view of the grant
request over time. The means by which these roles manage their state
is outside the scope of this specification.
_Processing_: When a request for access (Section 2) is received by
the AS, a new grant request is created and placed in the
_processing_ state by the AS. This state is also entered when an
existing grant request is updated by the client instance and when
interaction is completed. In this state, the AS processes the
context of the grant request to determine whether interaction with
the end user or RO is required for approval of the request. The
grant request has to exit this state before a response can be
returned to the client instance. If approval is required, the
request moves to the _pending_ state and the AS returns a continue
response (Section 3.1) along with any appropriate interaction
responses (Section 3.3). If no such approval is required, such as
when the client instance is acting on its own behalf or the AS can
determine that access has been fulfilled, the request moves to the
_approved_ state where access tokens for API access (Section 3.2)
and subject information (Section 3.4) can be issued to the client
instance. If the AS determines that no additional processing can
occur (such as a timeout or an unrecoverable error), the grant
request is moved to the _finalized_ state and is terminated.
_Pending_: When a request needs to be approved by a RO, or
interaction with the end user is required, the grant request
enters a state of _pending_. In this state, no access tokens can
be granted and no subject information can be released to the
client instance. While a grant request is in this state, the AS
seeks to gather the required consent and authorization (Section 4)
for the requested access. A grant request in this state is always
associated with a _continuation access token_ bound to the client
instance's key (see Section 3.1 for details of the continuation
access token). If no interaction finish method (Section 2.5.2) is
associated with this request, the client instance can send a
polling continue request (Section 5.2) to the AS. This returns a
continue response (Section 3.1) while the grant request remains in
this state, allowing the client instance to continue to check the
state of the pending grant request. If an interaction finish
method (Section 2.5.2) is specified in the grant request, the
client instance can continue the request after interaction
(Section 5.1) to the AS to move this request to the _processing_
state to be re-evaluated by the AS. Note that this occurs whether
the grant request has been approved or denied by the RO, since the
AS needs to take into account the full context of the request
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before determining the next step for the grant request. When
other information is made available in the context of the grant
request, such as through the asynchronous actions of the RO, the
AS moves this request to the _processing_ state to be re-
evaluated. If the AS determines that no additional interaction
can occur, such as all the interaction methods have timed out or a
revocation request (Section 5.4) is received from the client
instance, the grant request can be moved to the _finalized_ state.
_Approved_: When a request has been approved by an RO and no further
interaction with the end user is required, the grant request
enters a state of _approved_. In this state, responses to the
client instance can include access tokens for API access
(Section 3.2) and subject information (Section 3.4). If
continuation and updates are allowed for this grant request, the
AS can include the continuation response (Section 3.1). In this
state, post-interaction continuation requests (Section 5.1) are
not allowed and will result in an error, since all interaction is
assumed to have been completed. If the client instance sends a
polling continue request (Section 5.2) while the request is in
this state, new access tokens (Section 3.2) can be issued in the
response. Note that this always creates a new access token, but
any existing access tokens could be rotated and revoked using the
token management API (Section 6). The client instance can send an
update continuation request (Section 5.3) to modify the requested
access, causing the AS to move the request back to the
_processing_ state for re-evaluation. If the AS determines that
no additional tokens can be issued, and that no additional updates
are to be accepted (such as the continuation access tokens have
expired), the grant is moved to the _finalized_ state.
_Finalized_: After the access tokens are issued, if the AS does not
allow any additional updates on the grant request, the grant
request enters the _finalized_ state. This state is also entered
when an existing grant request is revoked by the client instance
(Section 5.4) or otherwise revoked by the AS (such as through out-
of-band action by the RO). This state can also be entered if the
AS determines that no additional processing is possible, for
example if the RO has denied the requested access or if
interaction is required but no compatible interaction methods are
available. Once in this state, no new access tokens can be
issued, no subject information can be returned, and no
interactions can take place. Once in this state, the grant
request is dead and cannot be revived. If future access is
desired by the client instance, a new grant request can be
created, unrelated to this grant request.
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While it is possible to deploy an AS in a stateless environment, GNAP
is a stateful protocol and such deployments will need a way to manage
the current state of the grant request in a secure and deterministic
fashion without relying on other components, such as the client
software, to keep track of the current state.
1.6. Sequences
GNAP can be used in a variety of ways to allow the core delegation
process to take place. Many portions of this process are
conditionally present depending on the context of the deployments,
and not every step in this overview will happen in all circumstances.
Note that a connection between roles in this process does not
necessarily indicate that a specific protocol message is sent across
the wire between the components fulfilling the roles in question, or
that a particular step is required every time. For example, for a
client instance interested in only getting subject information
directly, and not calling an RS, all steps involving the RS below do
not apply.
In some circumstances, the information needed at a given stage is
communicated out of band or is preconfigured between the components
or entities performing the roles. For example, one entity can
fulfill multiple roles, and so explicit communication between the
roles is not necessary within the protocol flow. Additionally some
components may not be involved in all use cases. For example, a
client instance could be calling the AS just to get direct user
information and have no need to get an access token to call an RS.
1.6.1. Overall Protocol Sequence
The following diagram provides a general overview of GNAP, including
many different optional phases and connections. The diagrams in the
following sections provide views of GNAP under more specific
circumstances. These additional diagrams use the same conventions as
the overall diagram below.
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.----------. .----------.
| End user | ~ ~ ~ ~ | Resource |
| | | Owner (RO) |
`----+-----` `-----+----`
║ ║
║ ║
(A) (B)
║ ║
║ ║
+-----+--+ ║ +------------+
| Client | (1) ║ | Resource |
|Instance| ║ | Server |
| | +-----------+---+ | (RS) |
| +--(2)-->| Authorization | | |
| |<-(3)---+ Server | | |
| | | (AS) | | |
| +--(4)-->| | | |
| |<-(5)---+ | | |
| | | | | |
| +---------------(6)------------->| |
| | | | (7) | |
| |<--------------(8)------------->| |
| | | | | |
| +--(9)-->| | | |
| |<-(10)--+ | | |
| | | | | |
| +---------------(11)------------>| |
| | | | (12) | |
| +--(13)->| | | |
| | | | | |
+--------+ +---------------+ +------------+
Legend
===== indicates a possible interaction with a human
----- indicates an interaction between protocol roles
~ ~ ~ indicates a potential equivalence or out-of-band
communication between roles
Figure 3: Figure 3: Overall sequence of GNAP
* (A) The end user interacts with the client instance to indicate a
need for resources on behalf of the RO. This could identify the
RS the client instance needs to call, the resources needed, or the
RO that is needed to approve the request. Note that the RO and
end user are often the same entity in practice, but GNAP makes no
general assumption that they are.
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* (1) The client instance determines what access is needed and which
AS to approach for access. Note that for most situations, the
client instance is pre-configured with which AS to talk to and
which kinds of access it needs, but some more dynamic processes
are discussed in Section 9.1.
* (2) The client instance requests access at the AS (Section 2).
* (3) The AS processes the request and determines what is needed to
fulfill the request (See Section 4). The AS sends its response to
the client instance (Section 3).
* (B) If interaction is required, the AS interacts with the RO
(Section 4) to gather authorization. The interactive component of
the AS can function using a variety of possible mechanisms
including web page redirects, applications, challenge/response
protocols, or other methods. The RO approves the request for the
client instance being operated by the end user. Note that the RO
and end user are often the same entity in practice, and many of
GNAP's interaction methods allow the client instance to facilitate
the end user interacting with the AS in order to fulfill the role
of the RO.
* (4) The client instance continues the grant at the AS (Section 5).
This action could occur in response to receiving a signal that
interaction has finished (Section 4.2) or through a periodic
polling mechanism, depending on the interaction capabilities of
the client software and the options active in the grant request.
* (5) If the AS determines that access can be granted, it returns a
response to the client instance (Section 3) including an access
token (Section 3.2) for calling the RS and any directly returned
information (Section 3.4) about the RO.
* (6) The client instance uses the access token (Section 7.2) to
call the RS.
* (7) The RS determines if the token is sufficient for the request
by examining the token. The means of the RS determining this
access are out of scope of this specification, but some options
are discussed in [I-D.ietf-gnap-resource-servers].
* (8) The client instance calls the RS (Section 7.2) using the
access token until the RS or client instance determine that the
token is no longer valid.
* (9) When the token no longer works, the client instance rotates
the access token (Section 6.1).
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* (10) The AS issues a new access token (Section 3.2) to the client
instance with the same rights as the original access token
returned in (5).
* (11) The client instance uses the new access token (Section 7.2)
to call the RS.
* (12) The RS determines if the new token is sufficient for the
request, as in (7).
* (13) The client instance disposes of the token (Section 6.2) once
the client instance has completed its access of the RS and no
longer needs the token.
The following sections and Appendix C contain specific guidance on
how to use GNAP in different situations and deployments. For
example, it is possible for the client instance to never request an
access token and never call an RS, just as it is possible to have no
end user involved in the delegation process.
1.6.2. Redirect-based Interaction
In this example flow, the client instance is a web application that
wants access to resources on behalf of the current user, who acts as
both the end user and the resource owner (RO). Since the client
instance is capable of directing the user to an arbitrary URI and
receiving responses from the user's browser, interaction here is
handled through front-channel redirects using the user's browser.
The redirection URI used for interaction is a service hosted by the
AS in this example. The client instance uses a persistent session
with the user to ensure the same user that is starting the
interaction is the user that returns from the interaction.
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+--------+ +--------+ .----.
| Client | | AS | | End |
|Instance| | | | User |
| |<=(1)== Start Session ===============================+ |
| | | | | |
| +--(2)--- Request Access --------->| | | |
| | | | | |
| |<-(3)-- Interaction Needed -------+ | | |
| | | | | |
| +==(4)== Redirect for Interaction ===================>| |
| | | | +------+
| | | |<==(5)==>| |
| | | | AuthN | RO |
| | | | | |
| | | |<==(6)==>| |
| | | | AuthZ +------+
| | | | | End |
| |<=(7)== Redirect for Continuation ===================+ User |
| | | | `----`
| +--(8)--- Continue Request ------->| |
| | | |
| |<-(9)----- Grant Access ----------+ |
| | | |
| | | | +--------+
| +--(10)-- Access API ---------------------------->| RS |
| | | | | |
| |<-(11)-- API Response ---------------------------| |
| | | | +--------+
+--------+ +--------+
Figure 4: Figure 4: Diagram of a redirect-based interaction
1. The client instance establishes a session with the user, in the
role of the end user.
2. The client instance requests access to the resource (Section 2).
The client instance indicates that it can redirect to an
arbitrary URI (Section 2.5.1.1) and receive a redirect from the
browser (Section 2.5.2.1). The client instance stores
verification information for its redirect in the session created
in (1).
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3. The AS determines that interaction is needed and responds
(Section 3) with a URI to send the user to (Section 3.3.1) and
information needed to verify the redirect (Section 3.3.5) in
(7). The AS also includes information the client instance will
need to continue the request (Section 3.1) in (8). The AS
associates this continuation information with an ongoing request
that will be referenced in (4), (6), and (8).
4. The client instance stores the verification and continuation
information from (3) in the session from (1). The client
instance then redirects the user to the URI (Section 4.1.1)
given by the AS in (3). The user's browser loads the
interaction redirect URI. The AS loads the pending request
based on the incoming URI generated in (3).
5. The user authenticates at the AS, taking on the role of the RO.
6. As the RO, the user authorizes the pending request from the
client instance.
7. When the AS is done interacting with the user, the AS redirects
the user back (Section 4.2.1) to the client instance using the
redirect URI provided in (2). The redirect URI is augmented
with an interaction reference that the AS associates with the
ongoing request created in (2) and referenced in (4). The
redirect URI is also augmented with a hash of the security
information provided in (2) and (3). The client instance loads
the verification information from (2) and (3) from the session
created in (1). The client instance calculates a hash
(Section 4.2.3) based on this information and continues only if
the hash validates. Note that the client instance needs to
ensure that the parameters for the incoming request match those
that it is expecting from the session created in (1). The
client instance also needs to be prepared for the end user never
being returned to the client instance and handle timeouts
appropriately.
8. The client instance loads the continuation information from (3)
and sends the interaction reference from (7) in a request to
continue the request (Section 5.1). The AS validates the
interaction reference ensuring that the reference is associated
with the request being continued.
9. If the request has been authorized, the AS grants access to the
information in the form of access tokens (Section 3.2) and
direct subject information (Section 3.4) to the client instance.
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10. The client instance uses the access token (Section 7.2) to call
the RS.
11. The RS validates the access token and returns an appropriate
response for the API.
An example set of protocol messages for this method can be found in
Appendix C.1.
1.6.3. User-code Interaction
In this example flow, the client instance is a device that is capable
of presenting a short, human-readable code to the user and directing
the user to enter that code at a known URI. The user enters the code
at a URI that is an interactive service hosted by the AS in this
example. The client instance is not capable of presenting an
arbitrary URI to the user, nor is it capable of accepting incoming
HTTP requests from the user's browser. The client instance polls the
AS while it is waiting for the RO to authorize the request. The
user's interaction is assumed to occur on a secondary device. In
this example it is assumed that the user is both the end user and RO.
Note that since the user is not assumed to be interacting with the
client instance through the same web browser used for interaction at
the AS, the user is not shown as being connected to the client
instance in this diagram.
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+--------+ +--------+ .----.
| Client | | AS | | End |
|Instance+--(1)--- Request Access --------->| | | User |
| | | | | |
| |<-(2)-- Interaction Needed -------+ | | |
| | | | | |
| +==(3)==== Display User Code ========================>| |
| | | | | |
| | | |<==(4)===+ |
| | | |Open URI | |
| | | | +------+
| | | |<==(5)==>| RO |
| | | | AuthN | |
| +--(9)--- Continue Request (A) --->| | | |
| | | |<==(6)==>| |
| |<-(10)-- Not Yet Granted (Wait) --+ | Code | |
| | | | | |
| | | |<==(7)==>| |
| | | | AuthZ | |
| | | | | |
| | | |<==(8)==>| |
| | | |Complete | |
| | | | +------+
| +--(11)-- Continue Request (B) --->| | | End |
| | | | | User |
| |<-(12)----- Grant Access ---------+ | `----`
| | | |
| | | | +--------+
| +--(13)-- Access API ---------------------------->| RS |
| | | | | |
| |<-(14)-- API Response ---------------------------+ |
| | | | +--------+
+--------+ +--------+
Figure 5: Figure 5: Diagram of a user-code-based interaction
1. The client instance requests access to the resource (Section 2).
The client instance indicates that it can display a user code
(Section 2.5.1.3).
2. The AS determines that interaction is needed and responds
(Section 3) with a user code to communicate to the user
(Section 3.3.3). The AS also includes information the client
instance will need to continue the request (Section 3.1) in (8)
and (10). The AS associates this continuation information with
an ongoing request that will be referenced in (4), (6), (8), and
(10).
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3. The client instance stores the continuation information from (2)
for use in (8) and (10). The client instance then communicates
the code to the user (Section 4.1.2) given by the AS in (2).
4. The users directs their browser to the user code URI. This URI
is stable and can be communicated via the client software's
documentation, the AS documentation, or the client software
itself. Since it is assumed that the RO will interact with the
AS through a secondary device, the client instance does not
provide a mechanism to launch the RO's browser at this URI.
5. The end user authenticates at the AS, taking on the role of the
RO.
6. The RO enters the code communicated in (3) to the AS. The AS
validates this code against a current request in process.
7. As the RO, the user authorizes the pending request from the
client instance.
8. When the AS is done interacting with the user, the AS indicates
to the RO that the request has been completed.
9. Meanwhile, the client instance loads the continuation
information stored at (3) and continues the request (Section 5).
The AS determines which ongoing access request is referenced
here and checks its state.
10. If the access request has not yet been authorized by the RO in
(6), the AS responds to the client instance to continue the
request (Section 3.1) at a future time through additional polled
continuation requests. This response can include updated
continuation information as well as information regarding how
long the client instance should wait before calling again. The
client instance replaces its stored continuation information
from the previous response (2). Note that the AS may need to
determine that the RO has not approved the request in a
sufficient amount of time and return an appropriate error to the
client instance.
11. The client instance continues to poll the AS (Section 5.2) with
the new continuation information in (9).
12. If the request has been authorized, the AS grants access to the
information in the form of access tokens (Section 3.2) and
direct subject information (Section 3.4) to the client instance.
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13. The client instance uses the access token (Section 7.2) to call
the RS.
14. The RS validates the access token and returns an appropriate
response for the API.
An example set of protocol messages for this method can be found in
Appendix C.2.
1.6.4. Asynchronous Authorization
In this example flow, the end user and RO roles are fulfilled by
different parties, and the RO does not interact with the client
instance. The AS reaches out asynchronously to the RO during the
request process to gather the RO's authorization for the client
instance's request. The client instance polls the AS while it is
waiting for the RO to authorize the request.
+--------+ +--------+ .----.
| Client | | AS | | RO |
|Instance+--(1)--- Request Access --------->| | | |
| | | | | |
| |<-(2)-- Not Yet Granted (Wait) ---+ | | |
| | | |<==(3)==>| |
| | | | AuthN | |
| +--(6)--- Continue Request (A) --->| | | |
| | | |<==(4)==>| |
| |<-(7)-- Not Yet Granted (Wait) ---+ | AuthZ | |
| | | | | |
| | | |<==(5)==>| |
| | | |Completed| |
| | | | | |
| +--(8)--- Continue Request (B) --->| | `----`
| | | |
| |<-(9)------ Grant Access ---------+ |
| | | |
| | | | +--------+
| +--(10)-- Access API ---------------------------->| RS |
| | | | | |
| |<-(11)-- API Response ---------------------------+ |
| | | | +--------+
+--------+ +--------+
Figure 6: Figure 6: Diagram of an asynchronous authorization
process, with no end user interaction
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1. The client instance requests access to the resource (Section 2).
The client instance does not send any interaction modes to the
server, indicating that it does not expect to interact with the
RO. The client instance can also signal which RO it requires
authorization from, if known, by using the subject request
(Section 2.2) and user request (Section 2.4) sections. It's
also possible for the AS to determine which RO needs to be
contacted by the nature of what access is being requested.
2. The AS determines that interaction is needed, but the client
instance cannot interact with the RO. The AS responds
(Section 3) with the information the client instance will need
to continue the request (Section 3.1) in (6) and (8), including
a signal that the client instance should wait before checking
the status of the request again. The AS associates this
continuation information with an ongoing request that will be
referenced in (3), (4), (5), (6), and (8).
3. The AS determines which RO to contact based on the request in
(1), through a combination of the user request (Section 2.4),
the subject request (Section 2.2), the access request
(Section 2.1), and other policy information. The AS contacts
the RO and authenticates them.
4. The RO authorizes the pending request from the client instance.
5. When the AS is done interacting with the RO, the AS indicates to
the RO that the request has been completed.
6. Meanwhile, the client instance loads the continuation
information stored at (2) and continues the request (Section 5).
The AS determines which ongoing access request is referenced
here and checks its state.
7. If the access request has not yet been authorized by the RO in
(6), the AS responds to the client instance to continue the
request (Section 3.1) at a future time through additional
polling. Note that this response is not an error message, since
no error has yet occurred. This response can include refreshed
credentials as well as information regarding how long the client
instance should wait before calling again. The client instance
replaces its stored continuation information from the previous
response (2). Note that the AS may need to determine that the
RO has not approved the request in a sufficient amount of time
and return an appropriate error to the client instance.
8. The client instance continues to poll the AS (Section 5.2) with
the new continuation information from (7).
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9. If the request has been authorized, the AS grants access to the
information in the form of access tokens (Section 3.2) and
direct subject information (Section 3.4) to the client instance.
10. The client instance uses the access token (Section 7.2) to call
the RS.
11. The RS validates the access token and returns an appropriate
response for the API.
An example set of protocol messages for this method can be found in
Appendix C.4.
Additional considerations for asynchronous interactions like this are
discussed in Section 13.36.
1.6.5. Software-only Authorization
In this example flow, the AS policy allows the client instance to
make a call on its own behalf, without the need for an RO to be
involved at runtime to approve the decision. Since there is no
explicit RO, the client instance does not interact with an RO.
+--------+ +--------+
| Client | | AS |
|Instance+--(1)--- Request Access --->| |
| | | |
| |<-(2)---- Grant Access -----+ |
| | | | +--------+
| +--(3)--- Access API ------------------->| RS |
| | | | | |
| |<-(4)--- API Response ------------------+ |
| | | | +--------+
+--------+ +--------+
Figure 7: Figure 7: Diagram of a software-only authorization,
with no end user or explicit resource owner
1. The client instance requests access to the resource (Section 2).
The client instance does not send any interaction modes to the
server.
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2. The AS determines that the request has been authorized based on
the identity of the client instance making the request and the
access requested (Section 2.1). The AS grants access to the
resource in the form of access tokens (Section 3.2) to the client
instance. Note that direct subject information (Section 3.4) is
not generally applicable in this use case, as there is no user
involved.
3. The client instance uses the access token (Section 7.2) to call
the RS.
4. The RS validates the access token and returns an appropriate
response for the API.
An example set of protocol messages for this method can be found in
Appendix C.3.
1.6.6. Refreshing an Expired Access Token
In this example flow, the client instance receives an access token to
access a resource server through some valid GNAP process. The client
instance uses that token at the RS for some time, but eventually the
access token expires. The client instance then gets a refreshed
access token by rotating the expired access token's value at the AS
using the token management API.
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+--------+ +--------+
| Client | | AS |
|Instance+--(1)--- Request Access ----------------->| |
| | | |
| |<-(2)--- Grant Access --------------------+ |
| | | |
| | +--------+ | |
| +--(3)--- Access Resource --->| RS | | |
| | | | | |
| |<-(4)--- Success Response ---+ | | |
| | | | | |
| | ( Time Passes ) | | | |
| | | | | |
| +--(5)--- Access Resource --->| | | |
| | | | | |
| |<-(6)--- Error Response -----+ | | |
| | +--------+ | |
| | | |
| +--(7)--- Rotate Token ------------------->| |
| | | |
| |<-(8)--- Rotated Token -------------------+ |
| | | |
+--------+ +--------+
Figure 8: Figure 8: Diagram of the process of refreshing an
access token
1. The client instance requests access to the resource (Section 2).
2. The AS grants access to the resource (Section 3) with an access
token (Section 3.2) usable at the RS. The access token response
includes a token management URI.
3. The client instance uses the access token (Section 7.2) to call
the RS.
4. The RS validates the access token and returns an appropriate
response for the API.
5. Time passes and the client instance uses the access token to call
the RS again.
6. The RS validates the access token and determines that the access
token is expired. The RS responds to the client instance with an
error.
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7. The client instance calls the token management URI returned in
(2) to rotate the access token (Section 6.1). The client
instance uses the access token (Section 7.2) in this call as well
as the appropriate key, see the token rotation section for
details.
8. The AS validates the rotation request including the signature and
keys presented in (7) and refreshes the access token
(Section 3.2.1). The response includes a new version of the
access token and can also include updated token management
information, which the client instance will store in place of the
values returned in (2).
1.6.7. Requesting Subject Information Only
In this scenario, the client instance does not call an RS and does
not request an access token. Instead, the client instance only
requests and is returned direct subject information (Section 3.4).
Many different interaction modes can be used in this scenario, so
these are shown only in the abstract as functions of the AS here.
+--------+ +--------+ .----.
| Client | | AS | | End |
|Instance| | | | User |
| +--(1)--- Request Access --------->| | | |
| | | | | |
| |<-(2)-- Interaction Needed -------+ | | |
| | | | | |
| +==(3)== Facilitate Interaction =====================>| |
| | | | +------+
| | | |<==(4)==>| RO |
| | | | AuthN | |
| | | | | |
| | | |<==(5)==>| |
| | | | AuthZ +------+
| | | | | End |
| |<=(6)== Signal Continuation =========================+ User |
| | | | `----`
| +--(7)--- Continue Request ------->| |
| | | |
| |<-(8)----- Grant Access ----------+ |
| | | |
+--------+ +--------+
Figure 9: Figure 9: Diagram of the process of requesting and
releasing subject information apart from access tokens
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1. The client instance requests access to subject information
(Section 2).
2. The AS determines that interaction is needed and responds
(Section 3) with appropriate information for facilitating user
interaction (Section 3.3).
3. The client instance facilitates the user interacting with the AS
(Section 4) as directed in (2).
4. The user authenticates at the AS, taking on the role of the RO.
5. As the RO, the user authorizes the pending request from the
client instance.
6. When the AS is done interacting with the user, the AS returns the
user to the client instance and signals continuation.
7. The client instance loads the continuation information from (2)
and calls the AS to continue the request (Section 5).
8. If the request has been authorized, the AS grants access to the
requested direct subject information (Section 3.4) to the client
instance. At this stage, the user is generally considered
"logged in" to the client instance based on the identifiers and
assertions provided by the AS. Note that the AS can restrict the
subject information returned and it might not match what the
client instance requested, see the section on subject information
for details.
1.6.8. Cross-User Authentication
In this scenario, the end user and resource owner are two different
people. Here, the client instance already knows who the end user is,
likely through a separate authentication process. The end user,
operating the client instance, needs to get subject information about
another person in the system, the RO. The RO is given an opportunity
to release this information using an asynchronous interaction method
with the AS. This scenario would apply, for instance, when the end
user is an agent in a call-center and the resource owner is a
customer authorizing the call center agent to access their account on
their behalf.
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.----. .----.
| End | | RO |
| User |<=================(1)== Identify RO ==================>| |
| | | |
| | +--------+ +--------+ | |
| +==(2)==>| Client | | AS | | |
| | RO ID |Instance| | | | |
| | | | | | | |
| | | +--(3)-- Req. ---->| | | |
| | | | | | | |
| | | |<-(4)-- Res. -----+ | | |
| | | | | |<==(5)==>| |
| | | | | | AuthN | |
| | | | | | | |
| | | | | |<==(6)==>| |
| | | | | | AuthZ | |
| | | | | | | |
| | | | | |<==(7)==>| |
| | | |<-(8)--- Finish --+ |Completed| |
| | | | | | | |
| | | +--(9)--- Cont. -->| | | |
| | | | | | | |
| | | |<-(10)-- Subj. ---+ | | |
| |<=(11)==+ | Info | | | |
| | Return | | | | | |
| | RO | | | | | |
| | Info | | | | | |
`----` +--------+ +--------+ `----`
Figure 10: Figure 10: Diagram of cross-user authorization, where
the end user and RO are different
Precondition: The end user is authenticated to the client instance,
and the client instance has an identifier representing the end user
that it can present to the AS. This identifier should be unique to
the particular session with the client instance and the AS. The
client instance is also known to the AS and allowed to access this
advanced functionality where the information of someone other than
the end user is returned to the client instance.
1. The RO communicates a human-readable identifier to the end user,
such as an email address or account number. This communication
happens out of band from the protocol, such as over the phone
between parties. Note that the RO is not interacting with the
client instance.
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2. The end user communicates the identifier to the client instance.
The means by which the identifier is communicated to the client
instance is out of scope for this specification.
3. The client instance requests access to subject information
(Section 2). The request includes the RO's identifier in the
subject information request (Section 2.2) sub_ids field, and the
end user's identifier in the user information field
(Section 2.4) of the request. The request includes no
interaction start methods, since the end user is not expected to
be the one interacting with the AS. The request does include
the push based interaction finish method (Section 2.5.2.2) to
allow the AS to signal to the client instance when the
interaction with the RO has concluded.
4. The AS sees that the identifier for the end user and subject
being requested are different. The AS determines that it can
reach out to the RO asynchronously for approval. While it is
doing so, the AS returns a continuation response (Section 3.1)
with a finish nonce to allow the client instance to continue the
grant request after interaction with the RO has concluded.
5. The AS contacts the RO and has them authenticate to the system.
The means for doing this are outside the scope of this
specification, but the identity of the RO is known from the
subject identifier sent in (3).
6. The RO is prompted to authorize the end user's request via the
client instance. Since the end user was identified in (3) via
the user field, the AS can show this information to the RO
during the authorization request.
7. The RO completes the authorization with the AS. The AS marks
the request as _approved_.
8. The RO pushes the interaction finish message (Section 4.2.2) to
the client instance. Note that in the case the RO cannot be
reached or the RO denies the request, the AS still sends the
interaction finish message to the client instance, after which
the client instance can negotiate next steps if possible.
9. The client instance validates the interaction finish message and
continues the grant request (Section 5.1).
10. The AS returns the RO's subject information (Section 3.4) to the
client instance.
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11. The client instance can display or otherwise utilize the RO's
user information in its session with the end user. Note that
since the client instance requested different sets of user
information in (3), the client instance does not conflate the
end user with the RO.
Additional considerations for asynchronous interactions like this are
discussed in Section 13.36.
2. Requesting Access
To start a request, the client instance sends an HTTP POST with a
JSON [RFC8259] document to the grant endpoint of the AS. The grant
endpoint is a URI that uniquely identifies the AS to client instances
and serves as the identifier for the AS. The document is a JSON
object where each field represents a different aspect of the client
instance's request. Each field is described in detail in a section
below.
access_token (object / array of objects): Describes the rights and
properties associated with the requested access token. REQUIRED
if requesting an access token. See Section 2.1.
subject (object): Describes the information about the RO that the
client instance is requesting to be returned directly in the
response from the AS. REQUIRED if requesting subject information.
See Section 2.2.
client (object / string): Describes the client instance that is
making this request, including the key that the client instance
will use to protect this request and any continuation requests at
the AS and any user-facing information about the client instance
used in interactions. REQUIRED. See Section 2.3.
user (object / string): Identifies the end user to the AS in a
manner that the AS can verify, either directly or by interacting
with the end user to determine their status as the RO. OPTIONAL.
See Section 2.4.
interact (object): Describes the modes that the client instance
supports for allowing the RO to interact with the AS and modes for
the client instance to receive updates when interaction is
complete. REQUIRED if interaction is supported. See Section 2.5.
Additional members of this request object can be defined by
extensions using the GNAP Grant Request Parameters Registry
(Section 11.2).
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A non-normative example of a grant request is below:
{
"access_token": {
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"dolphin-metadata"
]
},
"client": {
"display": {
"name": "My Client Display Name",
"uri": "https://example.net/client"
},
"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeL...."
}
}
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
},
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"subject": {
"sub_id_formats": ["iss_sub", "opaque"],
"assertion_formats": ["id_token"]
}
}
Sending a request to the grant endpoint creates a grant request in
the _processing_ state. The AS processes this request to determine
whether interaction or authorization are necessary (moving to the
_pending_ state), or if access can be granted immediately (moving to
the _approved_ state).
The request MUST be sent as a JSON object in the content of the HTTP
POST request with Content-Type application/json. A key proofing
mechanism MAY define an alternative content type, as long as the
content is formed from the JSON object. For example, the attached
JWS key proofing mechanism (see Section 7.3.4) places the JSON object
into the payload of a JWS wrapper, which is in turn sent as the
message content.
2.1. Requesting Access to Resources
If the client instance is requesting one or more access tokens for
the purpose of accessing an API, the client instance MUST include an
access_token field. This field MUST be an object (for a single
access token (Section 2.1.1)) or an array of these objects (for
multiple access tokens (Section 2.1.2)), as described in the
following sections.
2.1.1. Requesting a Single Access Token
To request a single access token, the client instance sends an
access_token object composed of the following fields.
access (array of objects/strings): Describes the rights that the
client instance is requesting for the access token to be used at
the RS. REQUIRED. See Section 8.
label (string): A unique name chosen by the client instance to refer
to the resulting access token. The value of this field is opaque
to the AS. If this field is included in the request, the AS MUST
include the same label in the token response (Section 3.2).
REQUIRED if used as part of a multiple access token request
(Section 2.1.2), OPTIONAL otherwise.
flags (array of strings): A set of flags that indicate desired
attributes or behavior to be attached to the access token by the
AS. OPTIONAL.
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The values of the flags field defined by this specification are as
follows:
"bearer": If this flag is included, the access token being requested
is a bearer token. If this flag is omitted, the access token is
bound to the key used by the client instance in this request (or
that key's most recent rotation) and the access token MUST be
presented using the same key and proofing method. Methods for
presenting bound and bearer access tokens are described in
Section 7.2. See Section 13.9 for additional considerations on
the use of bearer tokens.
Flag values MUST NOT be included more than once.
Additional flags can be defined by extensions using the GNAP Access
Token Flags Registry (Section 11.3).
In the following example, the client instance is requesting access to
a complex resource described by a pair of access request object.
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"access_token": {
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"delete"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
{
"type": "walrus-access",
"actions": [
"foo",
"bar"
],
"locations": [
"https://resource.other/"
],
"datatypes": [
"data",
"pictures",
"walrus whiskers"
]
}
],
"label": "token1-23"
}
If access is approved, the resulting access token is valid for the
described resource. Since the "bearer" flag is not provided in this
example, the token is bound to the client instance's key (or its most
recent rotation). The token is labeled "token1-23". The token
response structure is described in Section 3.2.1.
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2.1.2. Requesting Multiple Access Tokens
To request multiple access tokens to be returned in a single
response, the client instance sends an array of objects as the value
of the access_token parameter. Each object MUST conform to the
request format for a single access token request, as specified in
requesting a single access token (Section 2.1.1). Additionally, each
object in the array MUST include the label field, and all values of
these fields MUST be unique within the request. If the client
instance does not include a label value for any entry in the array,
or the values of the label field are not unique within the array, the
AS MUST return an "invalid_request" error (Section 3.6).
The following non-normative example shows a request for two separate
access tokens, token1 and token2.
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"access_token": [
{
"label": "token1",
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"dolphin-metadata"
]
},
{
"label": "token2",
"access": [
{
"type": "walrus-access",
"actions": [
"foo",
"bar"
],
"locations": [
"https://resource.other/"
],
"datatypes": [
"data",
"pictures",
"walrus whiskers"
]
}
],
"flags": [ "bearer" ]
}
]
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All approved access requests are returned in the multiple access
token response (Section 3.2.2) structure using the values of the
label fields in the request.
2.2. Requesting Subject Information
If the client instance is requesting information about the RO from
the AS, it sends a subject field as a JSON object. This object MAY
contain the following fields.
sub_id_formats (array of strings): An array of subject identifier
subject formats requested for the RO, as defined by
[I-D.ietf-secevent-subject-identifiers]. REQUIRED if subject
identifiers are requested.
assertion_formats (array of strings): An array of requested
assertion formats. Possible values include id_token for an OpenID
Connect ID Token ([OIDC]) and saml2 for a SAML 2 assertion
([SAML2]). Additional assertion formats are defined by the GNAP
Assertion Formats Registry (Section 11.5). REQUIRED if assertions
are requested.
sub_ids (array of objects): An array of subject identifiers
representing the subject for which information is being requested.
Each object is a subject identifier as defined by
[I-D.ietf-secevent-subject-identifiers]. All identifiers in the
sub_ids array MUST identify the same subject. If omitted, the AS
SHOULD assume that subject information requests are about the
current user and SHOULD require direct interaction or proof of
presence before releasing information. OPTIONAL.
Additional fields are defined in the GNAP Subject Information Request
Fields Registry (Section 11.4).
"subject": {
"sub_id_formats": [ "iss_sub", "opaque" ],
"assertion_formats": [ "id_token", "saml2" ]
}
The AS can determine the RO's identity and permission for releasing
this information through interaction with the RO (Section 4), AS
policies, or assertions presented by the client instance
(Section 2.4). If this is determined positively, the AS MAY return
the RO's information in its response (Section 3.4) as requested.
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Subject identifier types requested by the client instance serve only
to identify the RO in the context of the AS and can't be used as
communication channels by the client instance, as discussed in
Section 3.4.
2.3. Identifying the Client Instance
When sending new grant request to the AS, the client instance MUST
identify itself by including its client information in the client
field of the request and by signing the request with its unique key
as described in Section 7.3. Note that once a grant has been created
and is in the _pending_ or _accepted_ states, the AS can determine
which client is associated with the grant by dereferencing the
continuation access token sent in the continuation request
(Section 5). As a consequence, the client field is not sent or
accepted for continuation requests.
Client information MUST either be sent by value as an object or by
reference as a string (see Section 2.3.1).
When client instance information is sent by value, the client field
of the request consists of a JSON object with the following fields.
key (object / string): The public key of the client instance to be
used in this request as described in Section 7.1 or a reference to
a key as described in Section 7.1.1. REQUIRED.
class_id (string): An identifier string that the AS can use to
identify the client software comprising this client instance. The
contents and format of this field are up to the AS. OPTIONAL.
display (object): An object containing additional information that
the AS MAY display to the RO during interaction, authorization,
and management. OPTIONAL. (Section 2.3.2)
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"client": {
"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8..."
}
},
"class_id": "web-server-1234",
"display": {
"name": "My Client Display Name",
"uri": "https://example.net/client"
}
}
Additional fields are defined in the GNAP Client Instance Fields
Registry (Section 11.6).
Absent additional attestations, profiles, or trust mechanisms, both
the display and class_id fields are self-declarative, presented by
the client instance and the AS MUST exercise caution in their
interpretation, taking them as a hint but not as absolute truth. The
class_id field can be used in a variety of ways to help the AS make
sense of the particular context in which the client instance is
operating. In corporate environments, for example, different levels
of trust might apply depending on security policies. This field aims
to help the AS adjust its own access decisions for different classes
of client software. It is possible to configure a set of values and
rules during a pre-registration, and then have the client instances
provide them later in runtime as a hint to the AS. In other cases,
the client runs with a specific AS in mind, so a single hardcoded
value would acceptable (for instance, a set top box with a class_id
claiming to be "FooBarTV version 4"). While the client instance may
not have contacted the AS yet, the value of this class_id field can
be evaluated by the AS according to a broader context of dynamic use,
alongside other related information available elsewhere (for
instance, corresponding fields in a certificate). If the AS is not
able to interpret or validate the class_id field, it SHOULD return an
invalid_client error (Section 3.6) or interpret the request as if the
class_id were not present and not allow the set of privileges
associated with the class_id. See additional discussion of client
instance impersonation in Section 13.15.
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The client instance MUST prove possession of any presented key by the
proof mechanism associated with the key in the request. Key proofing
methods are defined in the GNAP Key Proofing Methods Registry
(Section 11.15) and an initial set of methods is described in
Section 7.3.
If the same public key is sent by value on different access requests,
the AS MUST treat these requests as coming from the same client
instance for purposes of identification, authentication, and policy
application. If the AS does not know the client instance's public
key ahead of time, the AS MAY accept or reject the request based on
attestations within the client request and other AS policy
mechanisms.
The client instance MUST NOT send a symmetric key by value in the
request, as doing so would expose the key directly instead of simply
proving possession of it. See considerations on symmetric keys in
Section 13.7.
The client instance's key MAY be pre-registered with the AS ahead of
time and associated with a set of policies and allowable actions
pertaining to that client. If this pre-registration includes other
fields that can occur in the client request object described in this
section, such as class_id or display, the pre-registered values MUST
take precedence over any values given at runtime. Additional fields
sent during a request but not present in a pre-registered client
instance record at the AS SHOULD NOT be added to the client's pre-
registered record. See additional considerations regarding client
instance impersonation in Section 13.15.
A client instance that is capable of talking to multiple AS's SHOULD
use a different key for each AS to prevent a class of mix-up attacks
as described in Section 13.31 unless other mechanisms can be used to
assure the identity of the AS for a given request.
2.3.1. Identifying the Client Instance by Reference
If the client instance has an instance identifier that the AS can use
to determine appropriate key information, the client instance can
send this instance identifier as a direct reference value in lieu of
the client object. The instance identifier MAY be assigned to a
client instance at runtime through a grant response (Section 3.5) or
MAY be obtained in another fashion, such as a static registration
process at the AS.
"client": "client-541-ab"
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When the AS receives a request with an instance identifier, the AS
MUST ensure that the key used to sign the request (Section 7.3) is
associated with the instance identifier.
If the AS does not recognize the instance identifier, the request
MUST be rejected with an invalid_client error (Section 3.6).
If the client instance is identified in this manner, the registered
key for the client instance MAY be a symmetric key known to the AS.
See considerations on symmetric keys in Section 13.7.
2.3.2. Providing Displayable Client Instance Information
If the client instance has additional information to display to the
RO during any interactions at the AS, it MAY send that information in
the "display" field. This field is a JSON object that declares
information to present to the RO during any interactive sequences.
name (string): Display name of the client software. RECOMMENDED.
uri (string): User-facing information about the client software,
such as a web page. This URI MUST be an absolute URI. OPTIONAL.
logo_uri (string) Display image to represent the client software.
This URI MUST be an absolute URI. The logo MAY be passed by value
by using a data: URI [RFC2397] referencing an image mediatype.
OPTIONAL.
"display": {
"name": "My Client Display Name",
"uri": "https://example.net/client",
"logo_uri": "data:image/png;base64,Eeww...="
}
Additional display fields are defined by the GNAP Client Instance
Display Fields Registry (Section 11.7).
The AS SHOULD use these values during interaction with the RO. The
values are for informational purposes only and MUST NOT be taken as
authentic proof of the client instance's identity or source. The AS
MAY restrict display values to specific client instances, as
identified by their keys in Section 2.3. See additional
considerations for displayed client information in Section 13.15 and
for the logo_uri in particular in Section 13.16.
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2.3.3. Authenticating the Client Instance
If the presented key is known to the AS and is associated with a
single instance of the client software, the process of presenting a
key and proving possession of that key is sufficient to authenticate
the client instance to the AS. The AS MAY associate policies with
the client instance identified by this key, such as limiting which
resources can be requested and which interaction methods can be used.
For example, only specific client instances with certain known keys
might be trusted with access tokens without the AS interacting
directly with the RO as in Appendix C.3.
The presentation of a key allows the AS to strongly associate
multiple successive requests from the same client instance with each
other. This is true when the AS knows the key ahead of time and can
use the key to authenticate the client instance, but also if the key
is ephemeral and created just for this series of requests. As such
the AS MAY allow for client instances to make requests with unknown
keys. This pattern allows for ephemeral client instances, such as
single-page applications, and client software with many individual
long-lived instances, such as mobile applications, to generate key
pairs per instance and use the keys within the protocol without
having to go through a separate registration step. The AS MAY limit
which capabilities are made available to client instances with
unknown keys. For example, the AS could have a policy saying that
only previously-registered client instances can request particular
resources, or that all client instances with unknown keys have to be
interactively approved by an RO.
2.4. Identifying the User
If the client instance knows the identity of the end user through one
or more identifiers or assertions, the client instance MAY send that
information to the AS in the "user" field. The client instance MAY
pass this information by value or by reference (See Section 2.4.1).
sub_ids (array of objects): An array of subject identifiers for the
end user, as defined by [I-D.ietf-secevent-subject-identifiers].
OPTIONAL.
assertions (array of objects) An array containing assertions as
objects each containing the assertion format and the assertion
value as the JSON string serialization of the assertion, as
defined in Section 3.4. OPTIONAL.
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"user": {
"sub_ids": [ {
"format": "opaque",
"id": "J2G8G8O4AZ"
} ],
"assertions": [ {
"format": "id_token",
"value": "eyj..."
} ]
}
Subject identifiers are hints to the AS in determining the RO and
MUST NOT be taken as authoritative statements that a particular RO is
present at the client instance and acting as the end user.
Assertions presented by the client instance SHOULD be validated by
the AS. While the details of such validation are outside the scope
of this specification, common validation steps include verifying the
signature of the assertion against a trusted signing key, verifying
the audience and issuer of the assertion map to expected values, and
verifying the time window for the assertion itself. However, note
that in many use cases, some of these common steps are relaxed. For
example, an AS acting as an identity provider (IdP) could expect that
assertions being presented using this mechanism were issued by the AS
to the client software. The AS would verify that the AS is the
issuer of the assertion, not the audience, and that the client
instance is instead the audience of the assertion. Similarly, an AS
might accept a recently-expired assertion in order to help bootstrap
a new session with a specific end user.
If the identified end user does not match the RO present at the AS
during an interaction step, and the AS is not explicitly allowing a
cross-user authorization, the AS SHOULD reject the request with an
unknown_user error (Section 3.6).
If the AS trusts the client instance to present verifiable assertions
or known subject identifiers, such as an opaque identifier issued by
the AS for this specific client instance, the AS MAY decide, based on
its policy, to skip interaction with the RO, even if the client
instance provides one or more interaction modes in its request.
See Section 13.30 for considerations that the AS has to make when
accepting and processing assertions from the client instance.
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2.4.1. Identifying the User by Reference
The AS can identify the current end user to the client instance with
a reference which can be used by the client instance to refer to the
end user across multiple requests. If the client instance has a
reference for the end user at this AS, the client instance MAY pass
that reference as a string. The format of this string is opaque to
the client instance.
"user": "XUT2MFM1XBIKJKSDU8QM"
One means of dynamically obtaining such a user reference is from the
AS returning an opaque subject identifier as described in
Section 3.4. Other means of configuring a client instance with a
user identifier are out of scope of this specification. The lifetime
and validity of these user references is determined by the AS and
this lifetime is not exposed to the client instance in GNAP. As
such, a client instance using such a user reference is likely to keep
using that reference until such a time as it stops working.
User reference identifiers are not intended to be human-readable user
identifiers or structured assertions. For the client instance to
send either of these, the client can use the full user request object
(Section 2.4) instead.
If the AS does not recognize the user reference, it MUST return an
unknown_user error (Section 3.6).
2.5. Interacting with the User
Often, the AS will require interaction with the RO (Section 4) in
order to approve a requested delegation to the client instance for
both access to resources and direct subject information. Many times
the end user using the client instance is the same person as the RO,
and the client instance can directly drive interaction with the end
user by facilitating the process through means such as redirection to
a URI or launching an application. Other times, the client instance
can provide information to start the RO's interaction on a secondary
device, or the client instance will wait for the RO to approve the
request asynchronously. The client instance could also be signaled
that interaction has concluded through a callback mechanism.
The client instance declares the parameters for interaction methods
that it can support using the interact field.
The interact field is a JSON object with three keys whose values
declare how the client can initiate and complete the request, as well
as provide hints to the AS about user preferences such as locale. A
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client instance MUST NOT declare an interaction mode it does not
support. The client instance MAY send multiple modes in the same
request. There is no preference order specified in this request. An
AS MAY respond to any, all, or none of the presented interaction
modes (Section 3.3) in a request, depending on its capabilities and
what is allowed to fulfill the request.
start (array of objects/strings): Indicates how the client instance
can start an interaction. REQUIRED. (Section 2.5.1)
finish (object): Indicates how the client instance can receive an
indication that interaction has finished at the AS. OPTIONAL.
(Section 2.5.2)
hints (object): Provides additional information to inform the
interaction process at the AS. OPTIONAL. (Section 2.5.3)
In this non-normative example, the client instance is indicating that
it can redirect (Section 2.5.1.1) the end user to an arbitrary URI
and can receive a redirect (Section 2.5.2.1) through a browser
request. Note that the client instance does not accept a push-style
callback. The pattern of using a redirect for both interaction start
and finish is common for web-based client software.
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
In this non-normative example, the client instance is indicating that
it can display a user code (Section 2.5.1.3) and direct the end user
to an arbitrary URI (Section 2.5.1.1), but it cannot accept a
redirect or push callback. This pattern is common for devices with
robust display capabilities but that expect the use of a secondary
device to facilitate end-user interaction with the AS, such as a set-
top box capable of displaying an interaction URL as a QR code.
"interact": {
"start": ["redirect", "user_code"]
}
In this non-normative example, the client instance is indicating that
it can not start any interaction with the end-user, but that the AS
can push an interaction finish message (Section 2.5.2.2) when
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authorization from the RO is received asynchronously. This pattern
is common for scenarios where a service needs to be authorized, but
the RO is able to be contacted separately from the GNAP transaction
itself, such as through a push notification or existing interactive
session on a secondary device.
"interact": {
"start": [],
"finish": {
"method": "push",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
If the client instance does not provide a suitable interaction
mechanism, the AS cannot contact the RO asynchronously, and the AS
determines that interaction is required, then the AS MUST return an
invalid_interaction error (Section 3.6) since the client instance
will be unable to complete the request without authorization.
2.5.1. Start Mode Definitions
If the client instance is capable of starting interaction with the
end user, the client instance indicates this by sending an array of
start modes under the start key. Each interaction start modes has a
unique identifying name. Interaction start modes are specified in
the array either by a string, which consists of the start mode name
on its own, or by a JSON object with the required field mode:
mode: The interaction start mode. REQUIRED.
Interaction start modes defined as objects MAY define additional
parameters to be required in the object.
The start array can contain both string-type and object-type modes.
This specification defines the following interaction start modes:
"redirect" (string): Indicates that the client instance can direct
the end user to an arbitrary URI for interaction. Section 2.5.1.1
"app" (string): Indicates that the client instance can launch an
application on the end user's device for interaction.
Section 2.5.1.2
"user_code" (string): Indicates that the client instance can
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communicate a human-readable short code to the end user for use
with a stable URI. Section 2.5.1.3
"user_code_uri" (string): Indicates that the client instance can
communicate a human-readable short code to the end user for use
with a short, dynamic URI. Section 2.5.1.4
Additional start modes are defined in the GNAP Interaction Start
Modes Registry (Section 11.8).
2.5.1.1. Redirect to an Arbitrary URI
If the client instance is capable of directing the end user to a URI
defined by the AS at runtime, the client instance indicates this by
including redirect in the array under the start key. The means by
which the client instance will activate this URI is out of scope of
this specification, but common methods include an HTTP redirect,
launching a browser on the end user's device, providing a scannable
image encoding, and printing out a URI to an interactive console.
While this URI is generally hosted at the AS, the client instance can
make no assumptions about its contents, composition, or relationship
to the grant endpoint URI.
"interact": {
"start": ["redirect"]
}
If this interaction mode is supported for this client instance and
request, the AS returns a redirect interaction response
Section 3.3.1. The client instance manages this interaction method
as described in Section 4.1.1.
See Section 13.29 for more considerations regarding the use of front-
channel communication techniques.
2.5.1.2. Open an Application-specific URI
If the client instance can open a URI associated with an application
on the end user's device, the client instance indicates this by
including app in the array under the start key. The means by which
the client instance determines the application to open with this URI
are out of scope of this specification.
"interact": {
"start": ["app"]
}
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If this interaction mode is supported for this client instance and
request, the AS returns an app interaction response with an app URI
payload (Section 3.3.2). The client instance manages this
interaction method as described in Section 4.1.4.
2.5.1.3. Display a Short User Code
If the client instance is capable of displaying or otherwise
communicating a short, human-entered code to the RO, the client
instance indicates this by including user_code in the array under the
start key. This code is to be entered at a static URI that does not
change at runtime. The client instance has no reasonable means to
communicate a dynamic URI to the RO, and so this URI is usually
communicated out of band to the RO through documentation or other
messaging outside of GNAP. While this URI is generally hosted at the
AS, the client instance can make no assumptions about its contents,
composition, or relationship to the grant endpoint URI.
"interact": {
"start": ["user_code"]
}
If this interaction mode is supported for this client instance and
request, the AS returns a user code as specified in Section 3.3.3.
The client instance manages this interaction method as described in
Section 4.1.2.
2.5.1.4. Display a Short User Code and URI
If the client instance is capable of displaying or otherwise
communicating a short, human-entered code along with a short, human-
entered URI to the RO, the client instance indicates this by
including user_code_uri in the array under the start key. This code
is to be entered at the dynamic URL given in the response. While
this URL is generally hosted at the AS, the client instance can make
no assumptions about its contents, composition, or relationship to
the grant endpoint URI.
"interact": {
"start": ["user_code_uri"]
}
If this interaction mode is supported for this client instance and
request, the AS returns a user code and interaction URL as specified
in Section 3.3.4. The client instance manages this interaction
method as described in Section 4.1.3.
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2.5.2. Interaction Finish Methods
If the client instance is capable of receiving a message from the AS
indicating that the RO has completed their interaction, the client
instance indicates this by sending the following members of an object
under the finish key.
method (string): The callback method that the AS will use to contact
the client instance. REQUIRED.
uri (string): Indicates the URI that the AS will either send the RO
to after interaction or send an HTTP POST request. This URI MAY
be unique per request and MUST be hosted by or accessible by the
client instance. This URI MUST be an absolute URI, and MUST NOT
contain any fragment component. If the client instance needs any
state information to tie to the front channel interaction
response, it MUST use a unique callback URI to link to that
ongoing state. The allowable URIs and URI patterns MAY be
restricted by the AS based on the client instance's presented key
information. The callback URI SHOULD be presented to the RO
during the interaction phase before redirect. REQUIRED for
redirect and push methods.
nonce (string): Unique ASCII string value to be used in the
calculation of the "hash" query parameter sent to the callback
URI, must be sufficiently random to be unguessable by an attacker.
MUST be generated by the client instance as a unique value for
this request. REQUIRED.
hash_method (string): An identifier of a hash calculation mechanism
to be used for the callback hash in Section 4.2.3, as defined in
the IANA Named Information Hash Algorithm Registry [HASH-ALG]. If
absent, the default value is sha-256. OPTIONAL.
This specification defines the following values for the method
parameter, with other values defined by the GNAP Interaction Finish
Methods Registry (Section 11.9):
"redirect": Indicates that the client instance can receive a
redirect from the end user's device after interaction with the RO
has concluded. Section 2.5.2.1
"push": Indicates that the client instance can receive an HTTP POST
request from the AS after interaction with the RO has concluded.
Section 2.5.2.2
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If interaction finishing is supported for this client instance and
request, the AS will return a nonce (Section 3.3.5) used by the
client instance to validate the callback. All interaction finish
methods MUST use this nonce to allow the client to verify the
connection between the pending interaction request and the callback.
GNAP does this through the use of the interaction hash, defined in
Section 4.2.3. All requests to the callback URI MUST be processed as
described in Section 4.2.
All interaction finish methods MUST require presentation of an
interaction reference for continuing this grant request. This means
that the interaction reference MUST be returned by the AS and MUST be
presented by the client as described in Section 5.1. The means by
which the interaction reference is returned to the client instance is
specific to the interaction finish method.
2.5.2.1. Receive an HTTP Callback Through the Browser
A finish method value of redirect indicates that the client instance
will expect a request from the RO's browser using the HTTP method GET
as described in Section 4.2.1.
The client instance's URI MUST be protected by HTTPS, be hosted on a
server local to the RO's browser ("localhost"), or use an
application-specific URI scheme that is loaded on the end user's
device.
"interact": {
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
Requests to the callback URI MUST be processed by the client instance
as described in Section 4.2.1.
Since the incoming request to the callback URI is from the RO's
browser, this method is usually used when the RO and end user are the
same entity. See Section 13.24 for considerations on ensuring the
incoming HTTP message matches the expected context of the request.
See Section 13.29 for more considerations regarding the use of front-
channel communication techniques.
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2.5.2.2. Receive an HTTP Direct Callback
A finish method value of push indicates that the client instance will
expect a request from the AS directly using the HTTP method POST as
described in Section 4.2.2.
The client instance's URI MUST be protected by HTTPS, be hosted on a
server local to the RO's browser ("localhost"), or use an
application-specific URI scheme that is loaded on the end user's
device.
"interact": {
"finish": {
"method": "push",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
Requests to the callback URI MUST be processed by the client instance
as described in Section 4.2.2.
Since the incoming request to the callback URI is from the AS and not
from the RO's browser, this request is not expected to have any
shared session information from the start method. See Section 13.24
and Section 13.23 for more considerations regarding the use of back-
channel and polling mechanisms like this.
2.5.3. Hints
The hints key is an object describing one or more suggestions from
the client instance that the AS can use to help drive user
interaction.
This specification defines the following properties under the hints
key:
ui_locales (array of strings): Indicates the end user's preferred
locales that the AS can use during interaction, particularly
before the RO has authenticated. OPTIONAL. Section 2.5.3.1
The following sections detail requests for interaction hints.
Additional interaction hints are defined in the GNAP Interaction
Hints Registry (Section 11.10).
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2.5.3.1. Indicate Desired Interaction Locales
If the client instance knows the end user's locale and language
preferences, the client instance can send this information to the AS
using the ui_locales field with an array of locale strings as defined
by [RFC5646].
"interact": {
"hints": {
"ui_locales": ["en-US", "fr-CA"]
}
}
If possible, the AS SHOULD use one of the locales in the array, with
preference to the first item in the array supported by the AS. If
none of the given locales are supported, the AS MAY use a default
locale.
3. Grant Response
In response to a client instance's request, the AS responds with a
JSON object as the HTTP content. Each possible field is detailed in
the sections below.
continue (object): Indicates that the client instance can continue
the request by making one or more continuation requests. REQUIRED
if continuation calls are allowed for this client instance on this
grant request. See Section 3.1.
access_token (object / array of objects): A single access token or
set of access tokens that the client instance can use to call the
RS on behalf of the RO. REQUIRED if an access token is included.
See Section 3.2.
interact (object): Indicates that interaction through some set of
defined mechanisms needs to take place. REQUIRED if interaction
is expected. See Section 3.3.
subject (object): Claims about the RO as known and declared by the
AS. REQUIRED if subject information is included. See
Section 3.4.
instance_id (string): An identifier this client instance can use to
identify itself when making future requests. OPTIONAL. See
Section 3.5.
error (object or string): An error code indicating that something
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has gone wrong. REQUIRED for an error condition. See
Section 3.6.
Additional fields can be defined by extensions to GNAP in the GNAP
Grant Response Parameters Registry (Section 11.11).
In this example, the AS is returning an interaction URI
(Section 3.3.1), a callback nonce (Section 3.3.5), and a continuation
response (Section 3.1).
NOTE: '\' line wrapping per RFC 8792
{
"interact": {
"redirect": "https://server.example.com/interact/4CF492ML\
VMSW9MKMXKHQ",
"finish": "MBDOFXG4Y5CVJCX821LH"
},
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU",
},
"uri": "https://server.example.com/tx"
}
}
In this example, the AS is returning a bearer access token
(Section 3.2.1) with a management URI and a subject identifier
(Section 3.4) in the form of an opaque identifier.
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"flags": ["bearer"],
"manage": {
"uri": "https://server.example.com/token/PRY5NM33O",
"access_token": {
"value": "B8CDFONP21-4TB8N6.BW7ONM"
}
}
},
"subject": {
"sub_ids": [ {
"format": "opaque",
"id": "J2G8G8O4AZ"
} ]
}
}
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In this example, the AS is returning set of subject identifiers
(Section 3.4), simultaneously as an opaque identifier, an email
address, and a decentralized identifier (DID).
{
"subject": {
"sub_ids": [ {
"format": "opaque",
"id": "J2G8G8O4AZ"
}, {
"format": "email",
"email": "user@example.com"
}, {
"format": "did",
"url": "did:example:123456"
} ]
}
}
The response MUST be sent as a JSON object in the content of the HTTP
response with Content-Type application/json, unless otherwise
specified by the specific response (e.g., an empty response with no
Content-Type).
The authorization server MUST include the HTTP Cache-Control response
header field [RFC9111] with a value set to "no-store".
3.1. Request Continuation
If the AS determines that the grant request can be continued by the
client instance, the AS responds with the continue field. This field
contains a JSON object with the following properties.
uri (string): The URI at which the client instance can make
continuation requests. This URI MAY vary per request, or MAY be
stable at the AS. This URI MUST be an absolute URI. The client
instance MUST use this value exactly as given when making a
continuation request (Section 5). REQUIRED.
wait (integer): The amount of time in integer seconds the client
instance MUST wait after receiving this request continuation
response and calling the continuation URI. The value SHOULD NOT
be less than five seconds, and omission of the value MUST be
interpreted as five seconds. RECOMMENDED.
access_token (object): A unique access token for continuing the
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request, called the "continuation access token". The value of
this property MUST be an object in the format specified in
Section 3.2.1. This access token MUST be bound to the client
instance's key used in the request and MUST NOT be a bearer token.
As a consequence, the flags array of this access token MUST NOT
contain the string bearer and the key field MUST be omitted. This
access token MUST NOT have a manage field. The client instance
MUST present the continuation access token in all requests to the
continuation URI as described in Section 7.2. REQUIRED.
{
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue",
"wait": 60
}
}
This field is REQUIRED if the grant request is in the _pending_
state, as the field contains the information needed by the client
request to continue the request as described in Section 5. Note that
the continuation access token is bound to the client instance's key,
and therefore the client instance MUST sign all continuation requests
with its key as described in Section 7.3 and MUST present the
continuation access token in its continuation request.
3.2. Access Tokens
If the AS has successfully granted one or more access tokens to the
client instance, the AS responds with the access_token field. This
field contains either a single access token as described in
Section 3.2.1 or an array of access tokens as described in
Section 3.2.2.
The client instance uses any access tokens in this response to call
the RS as described in Section 7.2.
The grant request MUST be in the _approved_ state to include this
field in the response.
3.2.1. Single Access Token
If the client instance has requested a single access token and the AS
has granted that access token, the AS responds with the
"access_token" field. The value of this field is an object with the
following properties.
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value (string): The value of the access token as a string. The
value is opaque to the client instance. The value MUST be limited
to the token68 character set defined in Section 11.2 of [HTTP] to
facilitate transmission over HTTP headers and within other
protocols without requiring additional encoding. REQUIRED.
label (string): The value of the label the client instance provided
in the associated token request (Section 2.1), if present.
REQUIRED for multiple access tokens or if a label was included in
the single access token request, OPTIONAL for a single access
token where no label was included in the request.
manage (object): Access information for the token management API for
this access token. The management URI for this access token. If
provided, the client instance MAY manage its access token as
described in Section 6. This management API is a function of the
AS and is separate from the RS the client instance is requesting
access to. OPTIONAL.
access (array of objects/strings): A description of the rights
associated with this access token, as defined in Section 8. If
included, this MUST reflect the rights associated with the issued
access token. These rights MAY vary from what was requested by
the client instance. REQUIRED.
expires_in (integer): The number of seconds in which the access will
expire. The client instance MUST NOT use the access token past
this time. Note that the access token MAY be revoked by the AS or
RS at any point prior to its expiration. OPTIONAL.
key (object / string): The key that the token is bound to, if
different from the client instance's presented key. The key MUST
be an object or string in a format described in Section 7.1. The
client instance MUST be able to dereference or process the key
information in order to be able to sign subsequent requests using
the access token (Section 7.2). When the key is provided by value
from the AS, the token shares some security properties with bearer
tokens as discussed in Section 13.38. It is RECOMMENDED that keys
returned for use with access tokens be key references as described
in Section 7.1.1 that the client instance can correlate to its
known keys. OPTIONAL.
flags (array of strings): A set of flags that represent attributes
or behaviors of the access token issued by the AS. OPTIONAL.
The value of the manage field is an object with the following
properties:
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uri (string): The URI of the token management API for this access
token. This URI MUST be an absolute URI. This URI MUST NOT include
the access token value and SHOULD be different for each access token
issued in a request and MUST NOT include the value of the access
token being managed. REQUIRED.
access_token (object): A unique access token for continuing the
request, called the "token management access token". The value of
this property MUST be an object in the format specified in
Section 3.2.1. This access token MUST be bound to the client
instance's key used in the request (or its most recent rotation)
and MUST NOT be a bearer token. As a consequence, the flags array
of this access token MUST NOT contain the string bearer and the
key field MUST be omitted. This access token MUST NOT have a
manage field. This access token MUST NOT have the same value as
the token it is managing. The client instance MUST present the
continuation access token in all requests to the continuation URI
as described in Section 7.2. REQUIRED.
The values of the flags field defined by this specification are as
follows:
"bearer": This flag indicates whether the token is a bearer token,
not bound to a key and proofing mechanism. If the bearer flag is
present, the access token is a bearer token, and the key field in
this response MUST be omitted. See Section 13.9 for additional
considerations on the use of bearer tokens.
"durable": Flag indicating a hint of AS behavior on token rotation.
If this flag is present, then the client instance can expect a
previously-issued access token to continue to work after it has
been rotated (Section 6.1) or the underlying grant request has
been modified (Section 5.3), resulting in the issuance of new
access tokens. If this flag is omitted, the client instance can
anticipate a given access token could stop working after token
rotation or grant request modification. Note that a token flagged
as durable can still expire or be revoked through any normal
means.
Flag values MUST NOT be included more than once.
Additional flags can be defined by extensions using the GNAP Access
Token Fields Registry (Section 11.3).
If the bearer flag and the key field in this response are omitted,
the token is bound the key used by the client instance (Section 2.3)
in its request for access. If the bearer flag is omitted, and the
key field is present, the token is bound to the key and proofing
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mechanism indicated in the key field. The means by which the AS
determines how to bind an access token to a key other than that
presented by the client instance is out of scope for this
specification, but common practices include pre-registering specific
keys in a static fashion.
The client software MUST reject any access token where the flags
field contains the bearer flag and the key field is present with any
value.
The following non-normative example shows a single access token bound
to the client instance's key used in the initial request, with a
management URI, and that has access to three described resources (one
using an object and two described by reference strings).
NOTE: '\' line wrapping per RFC 8792
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": {
"uri": "https://server.example.com/token/PRY5NM33O",
"access_token": {
"value": "B8CDFONP21-4TB8N6.BW7ONM"
}
},
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read", "dolphin-metadata"
]
}
The following non-normative example shows a single bearer access
token with access to two described resources.
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"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"flags": ["bearer"],
"access": [
"finance", "medical"
]
}
If the client instance requested a single access token
(Section 2.1.1), the AS MUST NOT respond with the multiple access
token structure.
3.2.2. Multiple Access Tokens
If the client instance has requested multiple access tokens and the
AS has granted at least one of them, the AS responds with the
"access_token" field. The value of this field is a JSON array, the
members of which are distinct access tokens as described in
Section 3.2.1. Each object MUST have a unique label field,
corresponding to the token labels chosen by the client instance in
the multiple access token request (Section 2.1.2).
In this non-normative example, two tokens are issued under the names
token1 and token2, and only the first token has a management URI
associated with it.
NOTE: '\' line wrapping per RFC 8792
"access_token": [
{
"label": "token1",
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": {
"uri": "https://server.example.com/token/PRY5NM33O",
"access_token": {
"value": "B8CDFONP21-4TB8N6.BW7ONM"
}
},
"access": [ "finance" ]
},
{
"label": "token2",
"value": "UFGLO2FDAFG7VGZZPJ3IZEMN21EVU71FHCARP4J1",
"access": [ "medical" ]
}
}
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Each access token corresponds to one of the objects in the
access_token array of the client instance's request (Section 2.1.2).
The AS MAY refuse to issue one or more of the requested access
tokens, for any reason. In such cases the refused token is omitted
from the response and all of the other issued access tokens are
included in the response under their respective requested labels. If
the client instance requested multiple access tokens (Section 2.1.2),
the AS MUST NOT respond with a single access token structure, even if
only a single access token is granted. In such cases, the AS MUST
respond with a multiple access token structure containing one access
token.
"access_token": [
{
"label": "token2",
"value": "8N6BW7OZB8CDFONP219-OS9M2PMHKUR64TBRP1LT0",
"manage": {
"uri": "https://server.example.com/token/PRY5NM33O",
"access_token": {
"value": "B8CDFONP21-4TB8N6.BW7ONM"
}
},
"access": [ "fruits" ]
}
]
The parameters of each access token are separate. For example, each
access token is expected to have a unique value and (if present)
label, and likely has different access rights associated with it.
Each access token could also be bound to different keys with
different proofing mechanisms.
3.3. Interaction Modes
If the client instance has indicated a capability to interact with
the RO in its request (Section 2.5), and the AS has determined that
interaction is both supported and necessary, the AS responds to the
client instance with any of the following values in the interact
field of the response. There is no preference order for interaction
modes in the response, and it is up to the client instance to
determine which ones to use. All supported interaction methods are
included in the same interact object.
redirect (string): Redirect to an arbitrary URI. REQUIRED if the
redirect interaction start mode is possible for this request. See
Section 3.3.1.
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app (string): Launch of an application URI. REQUIRED if the app
interaction start mode is possible for this request. See
Section 3.3.2.
user_code (string): Display a short user code. REQUIRED if the
user_code interaction start mode is possible for this request.
See Section 3.3.3.
user_code_uri (object): Display a short user code and URI. REQUIRED
if the user_code_uri interaction start mode is possible for this
request. Section 3.3.4
finish (string): A unique ASCII string value provided by the AS as a
nonce. This is used by the client instance to verify the callback
after interaction is completed. REQUIRED if the interaction
finish method requested by the client instance is possible for
this request. See Section 3.3.5.
expires_in (integer): The number of integer seconds after which this
set of interaction responses will expire and no longer be usable
by the client instance. If the interaction methods expire, the
client MAY re-start the interaction process for this grant request
by sending an update (Section 5.3) with a new interaction request
(Section 2.5) section. OPTIONAL. If omitted, the interaction
response modes returned do not expire but MAY be invalidated by
the AS at any time.
Additional interaction mode responses can be defined in the GNAP
Interaction Mode Responses Registry (Section 11.12).
The AS MUST NOT respond with any interaction mode that the client
instance did not indicate in its request. The AS MUST NOT respond
with any interaction mode that the AS does not support. Since
interaction responses include secret or unique information, the AS
SHOULD respond to each interaction mode only once in an ongoing
request, particularly if the client instance modifies its request
(Section 5.3).
The grant request MUST be in the _pending_ state to include this
field in the response.
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3.3.1. Redirection to an arbitrary URI
If the client instance indicates that it can redirect to an arbitrary
URI (Section 2.5.1.1) and the AS supports this mode for the client
instance's request, the AS responds with the "redirect" field, which
is a string containing the URI for the end user to visit. This URI
MUST be unique for the request and MUST NOT contain any security-
sensitive information such as user identifiers or access tokens.
"interact": {
"redirect": "https://interact.example.com/4CF492MLVMSW9MKMXKHQ"
}
The URI returned is a function of the AS, but the URI itself MAY be
completely distinct from the grant endpoint URI that the client
instance uses to request access (Section 2), allowing an AS to
separate its user-interactive functionality from its back-end
security functionality. The AS will need to dereference the specific
grant request and its information from the URI alone. If the AS does
not directly host the functionality accessed through the redirect
URI, then the means for the interaction functionality to communicate
with the rest of the AS are out of scope for this specification.
The client instance sends the end user to the URI to interact with
the AS. The client instance MUST NOT alter the URI in any way. The
means for the client instance to send the end user to this URI is out
of scope of this specification, but common methods include an HTTP
redirect, launching the system browser, displaying a scannable code,
or printing out the URI in an interactive console. See details of
the interaction in Section 4.1.1.
3.3.2. Launch of an application URI
If the client instance indicates that it can launch an application
URI (Section 2.5.1.2) and the AS supports this mode for the client
instance's request, the AS responds with the "app" field, which is a
string containing the URI for the client instance to launch. This
URI MUST be unique for the request and MUST NOT contain any security-
sensitive information such as user identifiers or access tokens.
"interact": {
"app": "https://app.example.com/launch?tx=4CF492MLV"
}
The means for the launched application to communicate with the AS are
out of scope for this specification.
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The client instance launches the URI as appropriate on its platform,
and the means for the client instance to launch this URI is out of
scope of this specification. The client instance MUST NOT alter the
URI in any way. The client instance MAY attempt to detect if an
installed application will service the URI being sent before
attempting to launch the application URI. See details of the
interaction in Section 4.1.4.
3.3.3. Display of a Short User Code
If the client instance indicates that it can display a short
user-typeable code (Section 2.5.1.3) and the AS supports this mode
for the client instance's request, the AS responds with a "user_code"
field. This field is string containing a unique short code that the
user can type into a web page. To facilitate usability, this string
MUST consist only of characters that can be easily typed by the end
user (such as ASCII letters or numbers) and MUST be processed by the
AS in a case-insensitive manner (see Section 4.1.2). The string MUST
be randomly generated so as to be unguessable by an attacker within
the time it is accepted. The time in which this code will be
accepted SHOULD be short lived, such as several minutes. It is
RECOMMENDED that this code be no more than eight characters in
length.
"interact": {
"user_code": "A1BC3DFF"
}
The client instance MUST communicate the "user_code" value to the end
user in some fashion, such as displaying it on a screen or reading it
out audibly. This code is used by the interaction component of the
AS as a means of identifying the pending grant request and does not
function as an authentication factor for the RO.
The URI that the end user is intended to enter the code into MUST be
stable, since the client instance is expected to have no means of
communicating a dynamic URI to the end user at runtime.
As this interaction mode is designed to facilitate interaction via a
secondary device, it is not expected that the client instance
redirect the end user to the URI where the code is entered. If the
client instance is capable of communicating an short arbitrary URI to
the end user for use with the user code, the client instance SHOULD
instead use the "user_code_uri" (Section 2.5.1.4) mode. If the
client instance is capable of communicating a long arbitrary URI to
the end user, such as through a scannable code, the client instance
SHOULD use the "redirect" (Section 2.5.1.1) mode for this purpose
instead of or in addition to the user code mode.
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See details of the interaction in Section 4.1.2.
3.3.4. Display of a Short User Code and URI
If the client instance indicates that it can display a short
user-typeable code (Section 2.5.1.3) and the AS supports this mode
for the client instance's request, the AS responds with a
"user_code_uri" object that contains the following members.
code (string): A unique short code that the end user can type into a
provided URI. To facilitate usability, this string MUST consist
only of characters that can be easily typed by the end user (such
as ASCII letters or numbers) and MUST be processed by the AS in a
case-insensitive manner (see Section 4.1.3). The string MUST be
randomly generated so as to be unguessable by an attacker within
the time it is accepted. The time in which this code will be
accepted SHOULD be short lived, such as several minutes. It is
RECOMMENDED that this code be no more than eight characters in
length. REQUIRED.
uri (string): The interaction URI that the client instance will
direct the RO to. This URI MUST be short enough to be
communicated to the end user by the client instance. It is
RECOMMENDED that this URI be short enough for an end user to type
in manually. The URI MUST NOT contain the code value. This URI
MUST be an absolute URI. REQUIRED.
"interact": {
"user_code_uri": {
"code": "A1BC3DFF",
"uri": "https://s.example/device"
}
}
The client instance MUST communicate the "code" to the end user in
some fashion, such as displaying it on a screen or reading it out
audibly. This code is used by the interaction component of the AS as
a means of identifying the pending grant request and does not
function as an authentication factor for the RO.
The client instance MUST also communicate the URI to the end user.
Since it is expected that the end user will continue interaction on a
secondary device, the URI needs to be short enough to allow the end
user to type or copy it to a secondary device without mistakes.
The URI returned is a function of the AS, but the URI itself MAY be
completely distinct from the grant endpoint URI that the client
instance uses to request access (Section 2), allowing an AS to
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separate its user-interactive functionality from its back-end
security functionality. If the AS does not directly host the
functionality accessed through the given URI, then the means for the
interaction functionality to communicate with the rest of the AS are
out of scope for this specification.
See details of the interaction in Section 4.1.2.
3.3.5. Interaction Finish
If the client instance indicates that it can receive a
post-interaction redirect or push at a URI (Section 2.5.2) and the AS
supports this mode for the client instance's request, the AS responds
with a finish field containing a nonce that the client instance will
use in validating the callback as defined in Section 4.2.
"interact": {
"finish": "MBDOFXG4Y5CVJCX821LH"
}
When the interaction is completed, the interaction component of the
AS MUST contact the client instance using the means defined by the
finish method as described in Section 4.2.
If the AS returns the finish field, the client instance MUST NOT
continue a grant request before it receives the associated
interaction reference on the callback URI. See details in
Section 4.2.
3.4. Returning Subject Information
If information about the RO is requested and the AS grants the client
instance access to that data, the AS returns the approved information
in the "subject" response field. The AS MUST return the subject
field only in cases where the AS is sure that the RO and the end user
are the same party. This can be accomplished through some forms of
interaction with the RO (Section 4).
This field is an object with the following properties.
sub_ids (array of objects): An array of subject identifiers for the
RO, as defined by [I-D.ietf-secevent-subject-identifiers].
REQUIRED if returning subject identifiers.
assertions (array of objects): An array containing assertions as
objects each containing the assertion object described below.
REQUIRED if returning assertions.
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updated_at (string): Timestamp as an [RFC3339] date string,
indicating when the identified account was last updated. The
client instance MAY use this value to determine if it needs to
request updated profile information through an identity API. The
definition of such an identity API is out of scope for this
specification. RECOMMENDED.
Assertion objects contain the following fields:
format (string): The assertion format. Possible formats include
id_token for an OpenID Connect ID Token ([OIDC]) and saml2 for a
SAML 2 assertion ([SAML2]). Additional assertion formats are
defined by the GNAP Assertion Formats Registry (Section 11.5).
REQUIRED.
value (string): The assertion value as the JSON string serialization
of the assertion. REQUIRED.
The following non-normative example contains an opaque identifier and
an OpenID Connect ID Token:
"subject": {
"sub_ids": [ {
"format": "opaque",
"id": "XUT2MFM1XBIKJKSDU8QM"
} ],
"assertions": [ {
"format": "id_token",
"value": "eyj..."
} ]
}
Subject identifiers returned by the AS SHOULD uniquely identify the
RO at the AS. Some forms of subject identifier are opaque to the
client instance (such as the subject of an issuer and subject pair),
while others forms (such as email address and phone number) are
intended to allow the client instance to correlate the identifier
with other account information at the client instance. The client
instance MUST NOT request or use any returned subject identifiers for
communication purposes (see Section 2.2). That is, a subject
identifier returned in the format of an email address or a phone
number only identifies the RO to the AS and does not indicate that
the AS has validated that the represented email address or phone
number in the identifier is suitable for communication with the
current user. To get such information, the client instance MUST use
an identity protocol to request and receive additional identity
claims. The details of an identity protocol and associated schema
are outside the scope of this specification.
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The AS MUST ensure that the returned subject information represents
the RO. In most cases, the AS will also ensure that the returned
subject information represents the end user authenticated
interactively at the AS. The AS SHOULD NOT re-use subject
identifiers for multiple different ROs.
The "sub_ids" and "assertions" response fields are independent of
each other. That is, a returned assertion MAY use a different
subject identifier than other assertions and subject identifiers in
the response. However, all subject identifiers and assertions
returned MUST refer to the same party.
The client instance MUST interpret all subject information in the
context of the AS from which the subject information is received, as
is discussed in Section 6 of [SP80063C]. For example, one AS could
return an email identifier of "user@example.com" for one RO, and a
different AS could return that same email identifier of
"user@example.com" for a completely different RO. A client instance
talking to both AS's needs to differentiate between these two
accounts by accounting for the AS source of each identifier and not
assuming that either has a canonical claim on the identifier without
additional configuration and trust agreements. Otherwise, a rogue AS
could exploit this to take over a targeted account asserted by a
different AS.
Extensions to this specification MAY define additional response
properties in the GNAP Subject Information Response Fields Registry
(Section 11.13).
The grant request MUST be in the _approved_ state to return this
field in the response.
See Section 13.30 for considerations that the client instance has to
make when accepting and processing assertions from the AS.
3.5. Returning a Dynamically-bound Client Instance Identifier
Many parts of the client instance's request can be passed as either a
value or a reference. The use of a reference in place of a value
allows for a client instance to optimize requests to the AS.
Some references, such as for the client instance's identity
(Section 2.3.1) or the requested resources (Section 8.1), can be
managed statically through an admin console or developer portal
provided by the AS or RS. The developer of the client software can
include these values in their code for a more efficient and compact
request.
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If desired, the AS MAY also generate and return an instance
identifier dynamically to the client instance in the response to
facilitate multiple interactions with the same client instance over
time. The client instance SHOULD use this instance identifier in
future requests in lieu of sending the associated data values in the
client field.
Dynamically generated client instance identifiers are string values
that MUST be protected by the client instance as secrets. Instance
identifier values MUST be unguessable and MUST NOT contain any
information that would compromise any party if revealed. Instance
identifier values are opaque to the client instance, and their
content is determined by the AS. The instance identifier MUST be
unique per client instance at the AS.
instance_id (string): A string value used to represent the
information in the client object that the client instance can use
in a future request, as described in Section 2.3.1. OPTIONAL.
This non-normative example shows an instance identifier along side an
issued access token.
{
"instance_id": "7C7C4AZ9KHRS6X63AJAO",
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0"
}
}
3.6. Error Response
If the AS determines that the request cannot be completed for any
reason, it responds to the client instance with an error field in the
response message. This field is either an object or a string.
When returned as an object, the object contains the following fields:
code (string): A single ASCII error code defining the error.
REQUIRED.
description (string): A human-readable string description of the
error intended for the developer of the client. OPTIONAL.
This specification defines the following code values:
"invalid_request": The request is missing a required parameter,
includes an invalid parameter value or is otherwise malformed.
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"invalid_client": The request was made from a client that was not
recognized or allowed by the AS, or the client's signature
validation failed.
"invalid_interaction" The client instance has provided an
interaction reference that is incorrect for this request or the
interaction modes in use have expired.
"invalid_flag" The flag configuration is not valid.
"invalid_rotation" The token rotation request is not valid.
"key_rotation_not_supported" The AS does not allow rotation of this
access token's key.
"invalid_continuation": The continuation of the referenced grant
could not be processed.
"user_denied": The RO denied the request.
"request_denied": The request was denied for an unspecified reason.
"unknown_user": The user presented in the request is not known to
the AS or does not match the user present during interaction.
"unknown_interaction": The interaction integrity could not be
established.
"too_fast": The client instance did not respect the timeout in the
wait response before the next call.
"too_many_attempts": A limit has been reached in the total number of
reasonable attempts. This number is either defined statically or
adjusted based on runtime conditions by the AS.
Additional error codes can be defined in the GNAP Error Codes
Registry (Section 11.14).
For example, if the RO denied the request while interacting with the
AS, the AS would return the following error when the client instance
tries to continue the grant request:
{
"error": {
"code": "user_denied",
"description": "The RO denied the request"
}
}
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Alternatively, the AS MAY choose to only return the error as codes
and provide the error as a string. Since the description field is
not intended to be machine-readable, the following response is
considered functionally equivalent to the previous example for the
purposes of the client software's understanding:
{
"error": "user_denied"
}
If an error state is reached but the grant is in the _pending_ state
(and therefore the client instance can continue), the AS MAY include
the continue field in the response along with the error, as defined
Section 3.1. This allows the client instance to modify its request
for access, potentially leading to prompting the RO again. Other
fields MUST NOT be included in the response.
4. Determining Authorization and Consent
When the client instance makes its initial request (Section 2) to the
AS for delegated access, it is capable of asking for several
different kinds of information in response:
* the access being requested, in the access_token request parameter
* the subject information being requested, in the subject request
parameter
* any additional requested information defined by extensions of this
protocol
When the grant request is in the _processing_ state, the AS
determines what authorizations and consents are required to fulfill
this requested delegation. The details of how the AS makes this
determination are out of scope for this document. However, there are
several common patterns defined and supported by GNAP for fulfilling
these requirements, including information sent by the client
instance, information gathered through the interaction process, and
information supplied by external parties. An individual AS can
define its own policies and processes for deciding when and how to
gather the necessary authorizations and consent, and how those are
applied to the grant request.
To facilitate the AS fulfilling this request, the client instance
sends information about the actions the client software can take,
including:
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* starting interaction with the end user, in the interact request
parameter
* receiving notification that interaction with the RO has concluded,
in the interact request parameter
* any additional capabilities defined by extensions of this protocol
The client instance can also supply information directly to the AS in
its request. The client instance can send several kinds of things,
including:
* the identity of the client instance, known from the keys or
identifiers in the client request parameter
* the identity of the end user, in the user request parameter
* any additional information presented by the client instance in the
request defined by extensions of this protocol
The AS will process this presented information in the context of the
client instance's request and can only trust the information as much
as it trusts the presentation and context of that request. If the AS
determines that the information presented in the initial request is
sufficient for granting the requested access, the AS MAY move the
grant request to the _approved_ state and return results immediately
in its response (Section 3) with access tokens and subject
information.
If the AS determines that additional runtime authorization is
required, the AS can either deny the request outright (if there is no
possible recovery) or move the grant request to the _pending_ state
and use a number of means at its disposal to gather that
authorization from the appropriate ROs, including for example:
* starting interaction with the end user facilitated by the client
software, such as a redirection or user code
* challenging the client instance through a challenge-response
mechanism
* requesting that the client instance present specific additional
information, such as a user's credential or an assertion
* contacting an RO through an out-of-band mechanism, such as a push
notification
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* executing an auxiliary software process through an out-of-band
mechanism, such as querying a digital wallet
The authorization and consent gathering process in GNAP is left
deliberately flexible to allow for a wide variety of different
deployments, interactions, and methodologies. In this process, the
AS can gather consent from the RO or apply the RO's policy as
necessitated by the access that has been requested. The AS can
sometimes determine which RO needs to prompt for consent based on
what has been requested by the client instance, such as a specific RS
record, an identified subject, or a request requiring specific access
such as approval by an administrator. In other cases, the request is
applied to whichever RO is present at the time of consent gathering.
This pattern is especially prevalent when the end user is sent to the
AS for an interactive session, during which the end user takes on the
role of the RO. In these cases, the end user is delegating their own
access as RO to the client instance.
The client instance can indicate that it is capable of facilitating
interaction with the end user, another party, or another piece of
software through its interaction start (Section 2.5.1) request.
Here, the AS usually needs to interact directly with the end user to
determine their identity, determine their status as an RO, and
collect their consent. If the AS has determined that authorization
is required and the AS can support one or more of the requested
interaction start methods, the AS returns the associated interaction
start responses (Section 3.3). The client instance SHOULD initiate
one or more of these interaction methods (Section 4.1) in order to
facilitate the granting of the request. If more than one interaction
start method is available, the means by which the client chooses
which methods to follow is out of scope of this specification.
After starting interaction, the client instance can then make a
continuation request (Section 5) either in response to a signal
indicating the finish of the interaction (Section 4.2), after a time-
based polling, or through some other method defined by an extension
of this specification through the GNAP Interaction Mode Responses
registry (Section 11.12).
If the grant request is not in the _approved_ state, the client
instance can repeat the interaction process by sending a grant update
request (Section 5.3) with new interaction (Section 2.5) methods.
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The client instance MUST use each interaction method at most once, if
a response can be detected. The AS MUST handle any interact request
as a one-time-use mechanism and SHOULD apply suitable timeouts to any
interaction start methods provided, including user codes and
redirection URIs. The client instance SHOULD apply suitable timeouts
to any interaction finish method.
In order to support client software deployed in disadvantaged network
conditions, the AS MAY allow for processing of the same interaction
method multiple times if the AS can determine that the request is
from the same party and the results are idempotent. For example, if
a client instance launches a redirect to the AS but does not receive
a response within a reasonable time, the client software can launch
the redirect again, assuming that it never reached the AS in the
first place. However, if the AS in question receives both requests,
it could mistakenly process them separately, creating an undefined
state for the client instance. If the AS can determine that both
requests come from the same origin or under the same session, and the
requests both came before any additional state change to the grant
occurs, the AS can reasonably conclude that the initial response was
not received and the same response can be returned to the client
instance.
If the AS instead has a means of contacting the RO directly, it could
do so without involving the client instance in its consent gathering
process. For example, the AS could push a notification to a known RO
and have the RO approve the pending request asynchronously. These
interactions can be through an interface of the AS itself (such as a
hosted web page), through another application (such as something
installed on the RO's device), through a messaging fabric, or any
other means.
When interacting with an RO, the AS can do anything it needs to
determine the authorization of the requested grant, including:
* authenticate the RO, through a local account or some other means
such as federated login
* validate the RO through presentation of claims, attributes, or
other information
* prompt the RO for consent for the requested delegation
* describe to the RO what information is being released, to whom,
and for what purpose
* provide warnings to the RO about potential attacks or negative
effects of allowing the information
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* allow the RO to modify the client instance's requested access,
including limiting or expanding that access
* provide the RO with artifacts such as receipts to facilitate an
audit trail of authorizations
* allow the RO to deny the requested delegation
The AS is also allowed to request authorization from more than one
RO, if the AS deems fit. For example, a medical record might need to
be released by both an attending nurse and a physician, or both
owners of a bank account need to sign off on a transfer request.
Alternatively, the AS could require N of M possible RO's to approve a
given request. In some circumstances, the AS could even determine
that the end user present during the interaction is not the
appropriate RO for a given request and reach out to the appropriate
RO asynchronously.
The RO is also allowed to define an automated policy at the AS to
determine which kind of end user can get access to the resource, and
under which condition. For instance, such a condition might require
the end user login and the acceptance of the RO's legal provisions.
Alternatively, client software could be acting without an end user,
and the RO's policy allows issuance of access tokens to specific
instances of that client software without human interaction.
While all of these cases are supported by GNAP, the details of their
implementation, and for determining which RO's or related policies
are required for a given request, are out of scope for this
specification.
4.1. Starting Interaction With the End User
When a grant request is in the _pending_ state, the interaction start
methods sent by the client instance can be used to facilitate
interaction with the end user. To initiate an interaction start
method indicated by the interaction start responses (Section 3.3)
from the AS, the client instance follows the steps defined by that
interaction start mode. The actions of the client instance required
for the interaction start modes defined in this specification are
described in the following sections. Interaction start modes defined
in extensions to this specification MUST define the expected actions
of the client software when that interaction start mode is used.
If the client instance does not start an interaction start mode
within an AS-determined amount of time, the AS MUST reject attempts
to use the interaction start modes. If the client instance has
already begun one interaction start mode and the interaction has been
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successfully completed, the AS MUST reject attempts to use other
interaction start modes. For example, if a user code has been
successfully entered for a grant request, the AS will need to reject
requests to an arbitrary redirect URI on the same grant request in
order to prevent an attacker from capturing and altering an active
authorization process.
4.1.1. Interaction at a Redirected URI
When the end user is directed to an arbitrary URI through the
"redirect" (Section 3.3.1) mode, the client instance facilitates
opening the URI through the end user's web browser. The client
instance could launch the URI through the system browser, provide a
clickable link, redirect the user through HTTP response codes, or
display the URI in a form the end user can use to launch such as a
multidimensional barcode. In all cases, the URI is accessed with an
HTTP GET request, and the resulting page is assumed to allow direct
interaction with the end user through an HTTP user agent. With this
method, it is common (though not required) for the RO to be the same
party as the end user, since the client instance has to communicate
the redirection URI to the end user.
In many cases, the URI indicates a web page hosted at the AS,
allowing the AS to authenticate the end user as the RO and
interactively provide consent. The URI value is used to identify the
grant request being authorized. If the URI cannot be associated with
a currently active request, the AS MUST display an error to the RO
and MUST NOT attempt to redirect the RO back to any client instance
even if a redirect finish method is supplied (Section 2.5.2.1). If
the URI is not hosted by the AS directly, the means of communication
between the AS and the service provided by this URI are out of scope
for this specification.
The client instance MUST NOT modify the URI when launching it, in
particular the client instance MUST NOT add any parameters to the
URI. The URI MUST be reachable from the end user's browser, though
the URI MAY be opened on a separate device from the client instance
itself. The URI MUST be accessible from an HTTP GET request and MUST
be protected by HTTPS, be hosted on a server local to the RO's
browser ("localhost"), or use an application-specific URI scheme that
is loaded on the end user's device.
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4.1.2. Interaction at the Static User Code URI
When the end user is directed to enter a short code through the
"user_code" (Section 3.3.3) mode, the client instance communicates
the user code to the end user and directs the end user to enter that
code at an associated URI. The client instance MAY format the user
code in such a way as to facilitate memorability and transfer of the
code, so long as this formatting does not alter the value as accepted
at the user code URI. For example, a client instance receiving the
user code "A1BC3DFF" could choose to display this to the user as
"A1BC 3DFF", breaking up the long string into two shorter strings.
When processing input codes, the AS MUST transform the input string
to remove invalid characters. In the above example, the space in
between the two parts would be removed upon its entry into the
interactive form at the user code URI. Additionally, the AS MUST
treat user input as case insensitive. For example, if the user
inputs the string "a1bc 3DFF", the AS will treat the input the same
as "A1BC3DFF". To facilitate this, it is RECOMMENDED that the AS use
only ASCII letters and numbers as valid characters for the user code.
It is RECOMMENDED that the AS choose from character values that are
easily copied and typed without ambiguity. For example, some glyphs
have multiple Unicode code points for the same visual character, and
the end-user could potentially type a different character than what
the AS has returned.
This mode is designed to be used when the client instance is not able
to communicate or facilitate launching an arbitrary URI. The
associated URI could be statically configured with the client
instance or in the client software's documentation. As a
consequence, these URIs SHOULD be short. The user code URI MUST be
reachable from the end user's browser, though the URI is usually
opened on a separate device from the client instance itself. The URI
MUST be accessible from an HTTP GET request and MUST be protected by
HTTPS, be hosted on a server local to the RO's browser ("localhost"),
or use an application-specific URI scheme that is loaded on the end
user's device.
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In many cases, the URI indicates a web page hosted at the AS,
allowing the AS to authenticate the end user as the RO and
interactively provide consent. The value of the user code is used to
identify the grant request being authorized. If the user code cannot
be associated with a currently active request, the AS MUST display an
error to the RO and MUST NOT attempt to redirect the RO back to any
client instance even if a redirect finish method is supplied
(Section 2.5.2.1). If the interaction component at the user code URI
is not hosted by the AS directly, the means of communication between
the AS and this URI, including communication of the user code itself,
are out of scope for this specification.
When the RO enters this code at the user code URI, the AS MUST
uniquely identify the pending request that the code was associated
with. If the AS does not recognize the entered code, the interaction
component MUST display an error to the user. If the AS detects too
many unrecognized code enter attempts, the interaction component
SHOULD display an error to the user indicating too many attempts and
MAY take additional actions such as slowing down the input
interactions. The user should be warned as such an error state is
approached, if possible.
4.1.3. Interaction at a Dynamic User Code URI
When the end user is directed to enter a short code through the
"user_code_uri" (Section 3.3.4) mode, the client instance
communicates the user code and associated URI to the end user and
directs the end user to enter that code at the URI. The client
instance MAY format the user code in such a way as to facilitate
memorability and transfer of the code, so long as this formatting
does not alter the value as accepted at the user code URI. For
example, a client instance receiving the user code "A1BC3DFF" could
choose to display this to the user as "A1BC 3DFF", breaking up the
long string into two shorter strings.
When processing input codes, the AS MUST transform the input string
to remove invalid characters. In the above example, the space in
between the two parts would be removed upon its entry into the
interactive form at the user code URI. Additionally, the AS MUST
treat user input as case insensitive. For example, if the user
inputs the string "a1bc 3DFF", the AS will treat the input the same
as "A1BC3DFF". To facilitate this, it is RECOMMENDED that the AS use
only ASCII letters and numbers as valid characters for the user code.
This mode is used when the client instance is not able to facilitate
launching a complex arbitrary URI but can communicate arbitrary
values like URIs. As a consequence, these URIs SHOULD be short
enough to allow the URI to be typed by the end user, such as a total
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length of 20 characters or fewer. The client instance MUST NOT
modify the URI when communicating it to the end user; in particular
the client instance MUST NOT add any parameters to the URI. The user
code URI MUST be reachable from the end user's browser, though the
URI is usually be opened on a separate device from the client
instance itself. The URI MUST be accessible from an HTTP GET request
and MUST be protected by HTTPS, be hosted on a server local to the
RO's browser ("localhost"), or use an application-specific URI scheme
that is loaded on the end user's device.
In many cases, the URI indicates a web page hosted at the AS,
allowing the AS to authenticate the end user as the RO and
interactively provide consent. The value of the user code is used to
identify the grant request being authorized. If the user code cannot
be associated with a currently active request, the AS MUST display an
error to the RO and MUST NOT attempt to redirect the RO back to any
client instance even if a redirect finish method is supplied
(Section 2.5.2.1). If the interaction component at the user code URI
is not hosted by the AS directly, the means of communication between
the AS and this URI, including communication of the user code itself,
are out of scope for this specification.
When the RO enters this code at the given URI, the AS MUST uniquely
identify the pending request that the code was associated with. If
the AS does not recognize the entered code, the interaction component
MUST display an error to the user. If the AS detects too many
unrecognized code enter attempts, the interaction component SHOULD
display an error to the user indicating too many attempts and MAY
take additional actions such as slowing down the input interactions.
The user should be warned as such an error state is approached, if
possible.
4.1.4. Interaction through an Application URI
When the client instance is directed to launch an application through
the "app" (Section 3.3.2) mode, the client launches the URI as
appropriate to the system, such as through a deep link or custom URI
scheme registered to a mobile application. The means by which the AS
and the launched application communicate with each other and perform
any of the required actions are out of scope for this specification.
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4.2. Post-Interaction Completion
If an interaction "finish" (Section 3.3.5) method is associated with
the current request, the AS MUST follow the appropriate method upon
completion of interaction in order to signal the client instance to
continue, except for some limited error cases discussed below. If a
finish method is not available, the AS SHOULD instruct the RO to
return to the client instance upon completion. In such cases, it is
expected that the client instance will poll the continuation endpoint
as described in Section 5.2.
The AS MUST create an interaction reference and associate that
reference with the current interaction and the underlying pending
request. The interaction reference value is an ASCII string
consisting of only unreserved characters per Section 2.3 of
[RFC3986]. The interaction reference value MUST be sufficiently
random so as not to be guessable by an attacker. The interaction
reference MUST be one-time-use to prevent interception and replay
attacks.
The AS MUST calculate a hash value based on the client instance and
AS nonces and the interaction reference, as described in
Section 4.2.3. The client instance will use this value to validate
the "finish" call.
All interaction finish methods MUST define a way to convey the hash
and interaction reference back to the client instance. When an
interaction finish method is used, the client instance MUST present
the interaction reference back to the AS as part of its continuation
request (Section 5.1).
Note that in many error cases, such as when the RO has denied access,
the "finish" method is still enacted by the AS. This pattern allows
the client instance to potentially recover from the error state by
modifying its request or providing additional information directly to
the AS in a continuation request. The AS MUST NOT follow the
"finish" method in the following circumstances:
* The AS has determined that any URIs involved with the finish
method are dangerous or blocked.
* The AS cannot determine which ongoing grant request is being
referenced.
* The ongoing grant request has been cancelled or otherwise blocked.
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4.2.1. Completing Interaction with a Browser Redirect to the Callback
URI
When using the redirect interaction finish method defined in
Section 2.5.2.1 and Section 3.3.5, the AS signals to the client
instance that interaction is complete and the request can be
continued by directing the RO (in their browser) back to the client
instance's redirect URI.
The AS secures this redirect by adding the hash and interaction
reference as query parameters to the client instance's redirect URI.
hash: The interaction hash value as described in Section 4.2.3.
REQUIRED.
interact_ref: The interaction reference generated for this
interaction. REQUIRED.
The means of directing the RO to this URI are outside the scope of
this specification, but common options include redirecting the RO
from a web page and launching the system browser with the target URI.
See Section 13.19 for considerations on which HTTP status code to use
when redirecting a request that potentially contains credentials.
NOTE: '\' line wrapping per RFC 8792
https://client.example.net/return/123455\
?hash=x-gguKWTj8rQf7d7i3w3UhzvuJ5bpOlKyAlVpLxBffY\
&interact_ref=4IFWWIKYBC2PQ6U56NL1
The client instance MUST be able to process a request on the URI. If
the URI is HTTP, the request MUST be an HTTP GET.
When receiving the request, the client instance MUST parse the query
parameters to extract the hash and interaction reference values. The
client instance MUST calculate and validate the hash value as
described in Section 4.2.3. If the hash validates, the client
instance sends a continuation request to the AS as described in
Section 5.1 using the interaction reference value received here. If
the hash does not validate, the client instance MUST NOT send the
interaction reference to the AS.
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4.2.2. Completing Interaction with a Direct HTTP Request Callback
When using the push interaction finish method defined in
Section 2.5.2.1 and Section 3.3.5, the AS signals to the client
instance that interaction is complete and the request can be
continued by sending an HTTP POST request to the client instance's
callback URI.
The HTTP message content is a JSON object consisting of the following
two fields:
hash (string): The interaction hash value as described in
Section 4.2.3. REQUIRED.
interact_ref (string) The interaction reference generated for this
interaction. REQUIRED.
POST /push/554321 HTTP/1.1
Host: client.example.net
Content-Type: application/json
{
"hash": "pjdHcrti02HLCwGU3qhUZ3wZXt8IjrV_BtE3oUyOuKNk",
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}
Since the AS is making an outbound connection to a URI supplied by an
outside party (the client instance), the AS MUST protect itself
against SSRF attacks when making this call as discussed in
Section 13.34.
When receiving the request, the client instance MUST parse the JSON
object and validate the hash value as described in Section 4.2.3. If
either fails, the client instance MUST return an unknown_interaction
error (Section 3.6). If the hash validates, the client instance
sends a continuation request to the AS as described in Section 5.1
using the interaction reference value received here.
4.2.3. Calculating the interaction hash
The "hash" parameter in the request to the client instance's callback
URI ties the front channel response to an ongoing request by using
values known only to the parties involved. This security mechanism
allows the client instance to protect itself against several kinds of
session fixation and injection attacks as discussed in Section 13.25
and related sections. The AS MUST always provide this hash, and the
client instance MUST validate the hash when received.
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To calculate the "hash" value, the party doing the calculation
creates a hash base string by concatenating the following values in
the following order using a single newline (0x0A) character to
separate them:
* the "nonce" value sent by the client instance in the interaction
"finish" section of the initial request (Section 2.5.2)
* the AS's nonce value from the interaction finish response
(Section 3.3.5)
* the "interact_ref" returned from the AS as part of the interaction
finish method (Section 4.2)
* the grant endpoint URI the client instance used to make its
initial request (Section 2)
There is no padding or whitespace before or after any of the lines,
and no trailing newline character. The following example shows a
constructed hash base string consisting of these four elements.
VJLO6A4CATR0KRO
MBDOFXG4Y5CVJCX821LH
4IFWWIKYB2PQ6U56NL1
https://server.example.com/tx
The party then hashes the bytes of the ASCII encoding of this string
with the appropriate algorithm based on the "hash_method" parameter
under the "finish" key of the interaction finish request
(Section 2.5.2). The resulting byte array from the hash function is
then encoded using URL-Safe Base64 with no padding [RFC4648]. The
resulting string is the hash value.
If provided, the "hash_method" value MUST be one of the hash name
strings defined in the IANA Named Information Hash Algorithm Registry
[HASH-ALG]. If the "hash_method" value is not present in the client
instance's request, the algorithm defaults to "sha-256".
For example, the "sha-256" hash method consists of hashing the input
string with the 256-bit SHA2 algorithm. The following is the encoded
"sha-256" hash of the above example hash base string.
x-gguKWTj8rQf7d7i3w3UhzvuJ5bpOlKyAlVpLxBffY
For another example, the "sha3-512" hash method consists of hashing
the input string with the 512-bit SHA3 algorithm. The following is
the encoded "sha3-512" hash of the above example hash base string.
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NOTE: '\' line wrapping per RFC 8792
pyUkVJSmpqSJMaDYsk5G8WCvgY91l-agUPe1wgn-cc5rUtN69gPI2-S_s-Eswed8iB4\
PJ_a5Hg6DNi7qGgKwSQ
5. Continuing a Grant Request
While it is possible for the AS to return an approved grant response
(Section 3) with all the client instance's requested information
(including access tokens (Section 3.2) and subject information
(Section 3.4)) immediately, it's more common that the AS will place
the grant request into the _pending_ state and require communication
with the client instance several times over the lifetime of a grant
request. This is often part of facilitating interaction (Section 4),
but it could also be used to allow the AS and client instance to
continue negotiating the parameters of the original grant request
(Section 2) through modification of the request.
The ability to continue an already-started request allows the client
instance to perform several important functions, including presenting
additional information from interaction, modifying the initial
request, and revoking a grant request in progress.
To enable this ongoing negotiation, the AS provides a continuation
API to the client software. The AS returns a continue field in the
response (Section 3.1) that contains information the client instance
needs to access this API, including a URI to access as well as a
special access token to use during the requests, called the
_continuation access token_.
All requests to the continuation API are protected by a bound
continuation access token. The continuation access token is bound to
the same key and method the client instance used to make the initial
request (or its most recent rotation). As a consequence, when the
client instance makes any calls to the continuation URI, the client
instance MUST present the continuation access token as described in
Section 7.2 and present proof of the client instance's key (or its
most recent rotation) by signing the request as described in
Section 7.3. The AS MUST validate the signature and ensure that it
is bound to the appropriate key for the continuation access token.
Access tokens other than the continuation access tokens MUST NOT be
usable for continuation requests. Conversely, continuation access
tokens MUST NOT be usable to make authorized requests to RS's, even
if co-located within the AS.
For example, here the client instance makes a POST request to a
unique URI and signs the request with HTTP Message Signatures:
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POST /continue/KSKUOMUKM HTTP/1.1
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Host: server.example.com
Content-Length: 0
Signature-Input: sig1=...
Signature: sig1=...
The AS MUST be able to tell from the client instance's request which
specific ongoing request is being accessed, using a combination of
the continuation URI and the continuation access token. If the AS
cannot determine a single active grant request to map the
continuation request to, the AS MUST return an invalid_continuation
error (Section 3.6).
For example, here the client instance makes a POST request to a
stable continuation endpoint URI with the interaction reference
(Section 5.1), includes the access token, and signs with HTTP Message
Signatures:
POST /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
{
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}
In this alternative example, the client instance had been provided a
continuation URI unique to this ongoing grant request:
POST /tx/rxgIIEVMBV-BQUO7kxbsp HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP eyJhbGciOiJub25lIiwidHlwIjoiYmFkIn0
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
{
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}
In both cases, the AS determines which grant is being asked for based
on the URI and continuation access token provided.
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If a wait parameter was included in the continuation response
(Section 3.1), the client instance MUST NOT call the continuation URI
prior to waiting the number of seconds indicated. If no wait period
is indicated, the client instance MUST NOT poll immediately and
SHOULD wait at least 5 seconds. If the client instance does not
respect the given wait period, the AS MUST return the too_fast error
(Section 3.6).
The response from the AS is a JSON object of a grant response and MAY
contain any of the fields described in Section 3, as described in
more detail in the sections below.
If the AS determines that the client instance can make further
requests to the continuation API, the AS MUST include a new
"continue" response (Section 3.1). The new continue response MUST
include a continuation access token as well, and this token SHOULD be
a new access token, invalidating the previous access token. If the
AS does not return a new continue response, the client instance MUST
NOT make an additional continuation request. If a client instance
does so, the AS MUST return an invalid_continuation error
(Section 3.6).
For continuation functions that require the client instance to send a
message content, the content MUST be a JSON object.
For all requests to the grant continuation API, the AS MAY make use
of long polling mechanisms such as discussed in [RFC6202]. That is
to say, instead of returning the current status immediately, the long
polling technique allows the AS additional time to process and
fulfill the request before returning the HTTP response to the client
instance. For example, when the AS receives a continuation request
but the grant request is in the _processing_ state, the AS could wait
until the grant request has moved to the _pending_ or _approved_
state before returning the response message.
5.1. Continuing After a Completed Interaction
When the AS responds to the client instance's finish method as in
Section 4.2.1, this response includes an interaction reference. The
client instance MUST include that value as the field interact_ref in
a POST request to the continuation URI.
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POST /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
{
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}
Since the interaction reference is a one-time-use value as described
in Section 4.2.1, if the client instance needs to make additional
continuation calls after this request, the client instance MUST NOT
include the interaction reference in subsequent calls. If the AS
detects a client instance submitting an interaction reference when
the request is not in the _pending_ state, the AS MUST return a
too_many_attempts error (Section 3.6) and SHOULD invalidate the
ongoing request by moving it to the _finalized_ state.
If the grant request is in the _approved_ state, the grant response
(Section 3) MAY contain any newly-created access tokens (Section 3.2)
or newly-released subject information (Section 3.4). The response
MAY contain a new "continue" response (Section 3.1) as described
above. The response SHOULD NOT contain any interaction responses
(Section 3.3).
If the grant request is in the _pending_ state, the grant response
(Section 3) MUST NOT contain access tokens or subject information,
and MAY contain a new interaction responses (Section 3.3) to any
interaction methods that have not been exhausted at the AS.
For example, if the request is successful in causing the AS to issue
access tokens and release opaque subject claims, the response could
look like this:
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{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": {
"uri": "https://server.example.com/token/PRY5NM33O",
"access_token": {
"value": "B8CDFONP21-4TB8N6.BW7ONM"
}
}
},
"subject": {
"sub_ids": [ {
"format": "opaque",
"id": "J2G8G8O4AZ"
} ]
}
}
With this example, the client instance can not make an additional
continuation request because a continue field is not included.
For another example, if the RO has denied the client instance's
request, the AS responds with the following response:
{
"error": "user_denied",
"continue": {
"access_token": {
"value": "33OMUKMKSKU80UPRY5NM"
},
"uri": "https://server.example.com/continue",
"wait": 30
}
}
In this example, the AS includes the continue field in the response.
Therefore, the client instance can continue the grant negotiation
process, perhaps modifying the request as discussed in Section 5.3.
5.2. Continuing During Pending Interaction (Polling)
When the client instance does not include a finish parameter, the
client instance will often need to poll the AS until the RO has
authorized the request. To do so, the client instance makes a POST
request to the continuation URI as in Section 5.1, but does not
include message content.
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POST /continue HTTP/1.1
Host: server.example.com
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
If the grant request is in the _approved_ state, the grant response
(Section 3) MAY contain any newly-created access tokens (Section 3.2)
or newly-released subject claims (Section 3.4). The response MAY
contain a new "continue" response (Section 3.1) as described above.
If a continue field is included, it SHOULD include a wait field to
facilitate a reasonable polling rate by the client instance. The
response SHOULD NOT contain interaction responses (Section 3.3).
If the grant request is in the _pending_ state, the grant response
(Section 3) MUST NOT contain access tokens or subject information,
and MAY contain a new interaction responses (Section 3.3) to any
interaction methods that have not been exhausted at the AS.
For example, if the request has not yet been authorized by the RO,
the AS could respond by telling the client instance to make another
continuation request in the future. In this example, a new, unique
access token has been issued for the call, which the client instance
will use in its next continuation request.
{
"continue": {
"access_token": {
"value": "33OMUKMKSKU80UPRY5NM"
},
"uri": "https://server.example.com/continue",
"wait": 30
}
}
If the request is successful in causing the AS to issue access tokens
and release subject information, the response could look like this
example:
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{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": {
"uri": "https://server.example.com/token/PRY5NM33O",
"access_token": {
"value": "B8CDFONP21-4TB8N6.BW7ONM"
}
}
},
"subject": {
"sub_ids": [ {
"format": "opaque",
"id": "J2G8G8O4AZ"
} ]
}
}
See Section 13.23 for considerations on polling for continuation
without an interaction finish method.
In error conditions, the AS responds to the client instance with the
error code as discussed in Section 3.6. For example, if the client
instance has polled too many times before the RO has approved the
request, the AS would respond with a message like this:
{
"error": "too_many_attempts"
}
Since this response does not include a continue section, the client
instance cannot continue to poll the AS for additional updates and
the grant request is _finalized_. If the client instance still needs
access to the resource, it will need to start with a new grant
request.
5.3. Modifying an Existing Request
The client instance might need to modify an ongoing request, whether
or not tokens have already been issued or subject information has
already been released. In such cases, the client instance makes an
HTTP PATCH request to the continuation URI and includes any fields it
needs to modify. Fields that aren't included in the request are
considered unchanged from the original request.
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A grant request associated with a modification request MUST be in the
_approved_ or _pending_ state. When the AS receives a valid
modification request, the AS MUST place the grant request into the
_processing_ state and re-evaluate the authorization in the new
context created by the update request, since the extent and context
of the request could have changed.
The client instance MAY include the access_token and subject fields
as described in Section 2.1 and Section 2.2. Inclusion of these
fields override any values in the initial request, which MAY trigger
additional requirements and policies by the AS. For example, if the
client instance is asking for more access, the AS could require
additional interaction with the RO to gather additional consent. If
the client instance is asking for more limited access, the AS could
determine that sufficient authorization has been granted to the
client instance and return the more limited access rights
immediately. If the grant request was previously in the _approved_
state, the AS could decide to remember the larger scale of access
rights associated with the grant request, allowing the client
instance to make subsequent requests of different subsets of granted
access. The details of this processing are out of scope for this
specification, but a one possible approach is as follows:
1. A client instance requests access to Foo, and is granted by the
RO. This results in an access token, AT1.
2. The client instance later modifies the grant request to include
Foo and Bar together. Since the client instance was previously
granted Foo under this grant request, the RO is prompted to allow
the client instance access to Foo and Bar together. This results
in a new access token, AT2 This access token has access to both
Foo and Bar. The rights of the original access token AT1 are not
modified.
3. The client instance makes another grant modification to ask only
for Bar. Since the client instance was previously granted Foo and
Bar together under this grant request, the RO is not prompted and
the access to Bar is granted in a new access token, AT3. This
new access token does not allow access to Foo.
4. The original access token AT1 expires and the client seeks a new
access token to replace it. The client instance makes another
grant modification to ask only for Foo. Since the client instance
was previously granted Foo and Bar together under this grant
request, the RO is not prompted and the access to Foo is granted
in a new access token, AT4. This new access token does not allow
access to Bar.
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All four access tokens are independent of each other and associated
with the same underlying grant request. Each of these access tokens
could possibly also be rotated using token management, if available.
For example, instead of asking for a new token to replace AT1, the
client instance could ask for a refresh of AT1 using the rotation
method of the token management API. This would result in a refreshed
AT1 with a different token value and expiration from the original AT1
but with the same access rights of allowing only access to Foo.
The client instance MAY include the interact field as described in
Section 2.5. Inclusion of this field indicates that the client
instance is capable of driving interaction with the end user, and
this field replaces any values from a previous request. The AS MAY
respond to any of the interaction responses as described in
Section 3.3, just like it would to a new request.
The client instance MAY include the user field as described in
Section 2.4 to present new assertions or information about the end
user. The AS SHOULD check that this presented user information is
consistent with any user information previously presented by the
client instance or otherwise associated with this grant request.
The client instance MUST NOT include the client section of the
request, since the client instance is assumed not to have changed.
Modification of client instance information, including rotation of
keys associated with the client instance, is outside the scope of
this specification.
The client instance MUST NOT include post-interaction responses such
as described in Section 5.1.
Modification requests MUST NOT alter previously-issued access tokens.
Instead, any access tokens issued from a continuation are considered
new, separate access tokens. The AS MAY revoke previously-issued
access tokens after a modification has occurred.
If the modified request can be granted immediately by the AS (the
grant request is in the _approved_ state), the grant response
(Section 3) MAY contain any newly-created access tokens (Section 3.2)
or newly-released subject claims (Section 3.4). The response MAY
contain a new "continue" response (Section 3.1) as described above.
If interaction can occur, the response SHOULD contain interaction
responses (Section 3.3) as well.
For example, a client instance initially requests a set of resources
using references:
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POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
{
"access_token": {
"access": [
"read", "write"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
},
"client": "987YHGRT56789IOLK"
}
Access is granted by the RO, and a token is issued by the AS. In its
final response, the AS includes a continue field, which includes a
separate access token for accessing the continuation API:
{
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue",
"wait": 30
},
"access_token": {
"value": "RP1LT0-OS9M2P_R64TB",
"access": [
"read", "write"
]
}
}
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This continue field allows the client instance to make an eventual
continuation call. Some time later, the client instance realizes
that it no longer needs "write" access and therefore modifies its
ongoing request, here asking for just "read" access instead of both
"read" and "write" as before.
PATCH /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
{
"access_token": {
"access": [
"read"
]
}
...
}
The AS replaces the previous access from the first request, allowing
the AS to determine if any previously-granted consent already
applies. In this case, the AS would determine that reducing the
breadth of the requested access means that new access tokens can be
issued to the client instance without additional interaction or
consent. The AS would likely revoke previously-issued access tokens
that had the greater access rights associated with them, unless they
had been issued with the durable flag.
{
"continue": {
"access_token": {
"value": "M33OMUK80UPRY5NMKSKU"
},
"uri": "https://server.example.com/continue",
"wait": 30
},
"access_token": {
"value": "0EVKC7-2ZKwZM_6N760",
"access": [
"read"
]
}
}
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For another example, the client instance initially requests read-only
access but later needs to step up its access. The initial request
could look like this example.
POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
{
"access_token": {
"access": [
"read"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
},
"client": "987YHGRT56789IOLK"
}
Access is granted by the RO, and a token is issued by the AS. In its
final response, the AS includes a continue field:
{
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue",
"wait": 30
},
"access_token": {
"value": "RP1LT0-OS9M2P_R64TB",
"access": [
"read"
]
}
}
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This allows the client instance to make an eventual continuation
call. The client instance later realizes that it now needs "write"
access in addition to the "read" access. Since this is an expansion
of what it asked for previously, the client instance also includes a
new interaction section in case the AS needs to interact with the RO
again to gather additional authorization. Note that the client
instance's nonce and callback are different from the initial request.
Since the original callback was already used in the initial exchange,
and the callback is intended for one-time-use, a new one needs to be
included in order to use the callback again.
PATCH /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
{
"access_token": {
"access": [
"read", "write"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/654321",
"nonce": "K82FX4T4LKLTI25DQFZC"
}
}
}
From here, the AS can determine that the client instance is asking
for more than it was previously granted, but since the client
instance has also provided a mechanism to interact with the RO, the
AS can use that to gather the additional consent. The protocol
continues as it would with a new request. Since the old access
tokens are good for a subset of the rights requested here, the AS
might decide to not revoke them. However, any access tokens granted
after this update process are new access tokens and do not modify the
rights of existing access tokens.
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5.4. Revoking a Grant Request
If the client instance wishes to cancel an ongoing grant request and
place it into the _finalized_ state, the client instance makes an
HTTP DELETE request to the continuation URI.
DELETE /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
If the request is successfully revoked, the AS responds with status
code HTTP 204 (No Content). The AS SHOULD revoke all associated
access tokens, if possible. The AS SHOULD disable all token rotation
and other token management functions on such access tokens, if
possible. Once the grant request is in the _finalized_ state, it
MUST NOT be moved to any other state.
6. Token Management
If an access token response includes the manage field as described in
Section 3.2.1, the client instance MAY call this URI to manage the
access token with the rotate and revoke actions defined in the
following sections. Other actions are undefined by this
specification.
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"flags": ["bearer"],
"manage": {
"uri": "https://server.example.com/token/PRY5NM33O",
"access_token": {
"value": "B8CDFONP21-4TB8N6.BW7ONM"
}
}
}
}
The token management access token issued under the manage field is
used to protect all calls to the token management API. The client
instance MUST present proof of the key associated with the token
along with the token management access token value.
The AS MUST validate the proof and ensure that it is associated with
the token management access token.
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The AS MUST uniquely identify the token being managed from the token
management URI, the token management access token, or a combination
of both.
6.1. Rotating the Access Token Value
If the client instance has an access token and that access token
expires, the client instance might want to rotate the access token to
a new value without expiration. Rotating an access token consists of
issuing a new access token in place of an existing access token, with
the same rights and properties as the original token, apart from an
updated token value and expiration time.
To rotate an access token, the client instance makes an HTTP POST to
the token management URI with no message content, sending the access
token in the authorization header as described in Section 7.2 and
signing the request with the appropriate key.
POST /token/PRY5NM33O HTTP/1.1
Host: server.example.com
Authorization: GNAP B8CDFONP21-4TB8N6.BW7ONM
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
The client instance can not request to alter the access rights
associated with the access token during a rotation request. To get
an access token with different access rights for this grant request,
the client instance has to call the continuation API's update
(Section 5.3) functionality to get a new access token. The client
instance can also create a new grant request with the required access
rights.
The AS validates that the token management access token presented is
associated with the management URI, that the AS issued the token to
the given client instance, and that the presented key is the correct
key for the token management access token. The AS determines which
access token is being rotated from the token management URI, the
token management access token, or both.
If the token is validated and the key is appropriate for the request,
the AS MUST invalidate the current access token value associated with
this URI, if possible. Note that stateless access tokens can make
proactive revocation difficult within a system, see Section 13.32.
For successful rotations, the AS responds with an HTTP 200 with a
JSON-formatted message content consisting of the rotated access token
in the access_token field described in Section 3.2.1. The value of
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the access token MUST NOT be the same as the current value of the
access token used to access the management API. The response MUST
include an access token management URI, and the value of this URI MAY
be different from the URI used by the client instance to make the
rotation call. The client instance MUST use this new URI to manage
the rotated access token.
The access rights in the access array for the rotated access token
MUST be included in the response and MUST be the same as the token
before rotation.
NOTE: '\' line wrapping per RFC 8792
{
"access_token": {
"value": "FP6A8H6HY37MH13CK76LBZ6Y1UADG6VEUPEER5H2",
"manage": {
"uri": "https://server.example.com/token/PRY5NM33O",
"access_token": {
"value": "B8CDFONP21-4TB8N6.BW7ONM"
}
},
"expires_in": 3600,
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read", "dolphin-metadata"
]
}
}
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If the AS is unable or unwilling to rotate the value of the access
token, the AS responds with an invalid_rotation error (Section 3.6).
Upon receiving such an error, the client instance MUST consider the
access token to not have changed its state.
6.1.1. Binding a New Key to the Rotated Access Token
If the client instance wishes to bind a new presentation key to an
access token, the client instance MUST present both the new key and
the proof of previous key material in the access token rotation
request. The client instance makes an HTTP POST as a JSON object
with the following field:
key: The new key value or reference in the format described in
Section 7.1. Note that keys passed by value are always public
keys. REQUIRED when doing key rotation.
The proof method and parameters for the new key MUST be the same as
those established for the previous key.
The client instance MUST prove possession of both the currently-bound
key and the newly-requested key simultaneously in the rotation
request. Specifically, the signature from the previous key MUST
cover the value or reference of the new key, and the signature of the
new key MUST cover the signature value of the old key. The means of
doing so varies depending on the proofing method in use. For
example, the HTTP Message Signatures proofing method uses multiple
signatures in the request as described in Section 7.3.1.1, as shown
in this example.
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POST /token/PRY5NM33O HTTP/1.1
Host: server.example.com
Authorization: GNAP B8CDFONP21-4TB8N6.BW7ONM
Signature-Input: sig1=..., sig2=("signature";key=sig1)...
Signature: sig1=..., sig2=...
Content-Digest: sha-256=...
{
"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-2",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
}
}
}
Failure to present the appropriate proof of either the new key or the
previous key for the access token, as defined by the proof method,
MUST result in an invalid_rotation error code from the AS
(Section 3.6).
An attempt to change the proof method or parameters, including an
attempt to rotate the key of a bearer token (which has no key), MUST
result in an invalid_rotation error code returned from the AS
(Section 3.6).
If the AS does not allow rotation of the access token's key for any
reason, including but not limited to lack of permission for this
client instance or lack of capability by the AS, the AS MUST return a
key_rotation_not_supported error code (Section 3.6).
6.2. Revoking the Access Token
If the client instance wishes to revoke the access token proactively,
such as when a user indicates to the client instance that they no
longer wish for it to have access or the client instance application
detects that it is being uninstalled, the client instance can use the
token management URI to indicate to the AS that the AS SHOULD
invalidate the access token for all purposes.
The client instance makes an HTTP DELETE request to the token
management URI, presenting the access token and signing the request
with the appropriate key.
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DELETE /token/PRY5NM33O HTTP/1.1
Host: server.example.com
Authorization: GNAP B8CDFONP21-4TB8N6.BW7ONM
Signature-Input: sig1=...
Signature: sig1=...
If the key presented is associated with the token (or the client
instance, in the case of a bearer token), the AS MUST invalidate the
access token, if possible, and return an HTTP 204 response code.
204 No Content
Though the AS MAY revoke an access token at any time for any reason,
the token management function is specifically for the client
instance's use. If the access token has already expired or has been
revoked through other means, the AS SHOULD honor the revocation
request to the token management URI as valid, since the end result is
still the token not being usable.
7. Securing Requests from the Client Instance
In GNAP, the client instance secures its requests to an AS and RS by
presenting an access token, presenting proof of a key that it
possesses (aka, a "key proof"), or both an access token and key proof
together.
* When an access token is used with a key proof, this is a bound
token request. This type of request is used for calls to the RS
as well as the AS during grant negotiation.
* When a key proof is used with no access token, this is a non-
authorized signed request. This type of request is used for calls
to the AS to initiate a grant negotiation.
* When an access token is used with no key proof, this is a bearer
token request. This type of request is used only for calls to the
RS, and only with access tokens that are not bound to any key as
described in Section 3.2.1.
* When neither an access token nor key proof are used, this is an
unsecured request. This type of request is used optionally for
calls to the RS as part of an RS-first discovery process as
described in Section 9.1.
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7.1. Key Formats
Several different places in GNAP require the presentation of key
material by value or by reference. Key material sent by value is
sent using a JSON object with several fields described in this
section.
All keys are associated with a specific key proofing method. The
proofing method associated with the key is indicated using the proof
field of the key object.
proof (string or object): The form of proof that the client instance
will use when presenting the key. The valid values of this field
and the processing requirements for each are detailed in
Section 7.3. REQUIRED.
A key presented by value MUST be a public key and MUST be presented
in one and only one supported format, as discussed in Section 13.35.
Note that while most formats present the full value of the public
key, some formats present a value cryptographically derived from the
public key. See additional discussion of the presentation of public
keys in Section 13.7.
jwk (object): The public key and its properties represented as a
JSON Web Key [RFC7517]. A JWK MUST contain the alg (Algorithm)
and kid (Key ID) parameters. The alg parameter MUST NOT be
"none". The x5c (X.509 Certificate Chain) parameter MAY be used
to provide the X.509 representation of the provided public key.
OPTIONAL.
cert (string): PEM serialized value of the certificate used to sign
the request, with optional internal whitespace per [RFC7468]. The
PEM header and footer are optionally removed. OPTIONAL.
cert#S256 (string): The certificate thumbprint calculated as per
OAuth-MTLS [RFC8705] in base64 URL encoding. Note that this
format does not include the full public key. OPTIONAL.
Additional key formats are defined in the GNAP Key Formats Registry
(Section 11.16).
This non-normative example shows a single key presented in two
different formats. This example key is intended to be used with the
HTTP Message Signatures (Section 7.3.1) proofing mechanism, as
indicated by the httpsig value of the proof field.
As a JSON Web Key:
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"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
}
}
As a certificate in PEM format:
"key": {
"proof": "httpsig",
"cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFA..."
}
When the key is presented in GNAP, proof of this key material MUST be
used to bind the request, the nature of which varies with the
location in the protocol the key is used. For a key used as part of
a client instance's initial request in Section 2.3, the key value
represents the client instance's public key, and proof of that key
MUST be presented in that request. For a key used as part of an
access token response in Section 3.2.1, the proof of that key MUST be
used when the client instance later presents the access token to the
RS.
7.1.1. Key References
Keys in GNAP can also be passed by reference such that the party
receiving the reference will be able to determine the appropriate
keying material for use in that part of the protocol. Key references
are a single opaque string.
"key": "S-P4XJQ_RYJCRTSU1.63N3E"
Keys referenced in this manner MAY be shared symmetric keys. See the
additional considerations for symmetric keys in Section 13.7. The
key reference MUST NOT contain any unencrypted private or shared
symmetric key information.
Keys referenced in this manner MUST be bound to a single proofing
mechanism.
The means of dereferencing this reference to a key value and proofing
mechanism are out of scope for this specification. Commonly, key
references are created by the AS and are not necessarily needed to be
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understood by the client. These types of key references are an
internal reference to the AS, such as an identifier of a record in a
database. In other applications, it can be useful to use key
references that are resolvable by both clients and AS, which could be
accomplished by a client publishing a public key at a URI, for
example. For interoperability, this method could later be described
as an extension, but doing so is out of scope for this specification.
7.1.2. Key Protection
The security of GNAP relies on the cryptographic security of the keys
themselves. When symmetric keys are used in GNAP, a key management
system or secure key derivation mechanism MUST be used to supply the
keys. Symmetric keys MUST NOT be a human memorable password or a
value derived from one. Symmetric keys MUST NOT be passed by value
from the client instance to the AS.
Additional security considerations apply when rotating keys
(Section 13.22).
7.2. Presenting Access Tokens
Access tokens are issued to client instances in GNAP to allow the
client instance to make an authorized call to an API. The method the
client instance uses to send an access token depends on whether the
token is bound to a key, and if so which proofing method is
associated with the key. This information is conveyed by the key
parameter and the bearer flag in the access token response structure
(Section 3.2.1).
If the flags field does not contain the bearer flag and the key is
absent, the access token MUST be sent using the same key and proofing
mechanism that the client instance used in its initial request (or
its most recent rotation).
If the flags field does not contain the bearer flag and the key value
is an object as described in Section 7.1, the access token MUST be
sent using the key and proofing mechanism defined by the value of the
proof field within the key object.
The access token MUST be sent using the HTTP "Authorization" request
header field and the "GNAP" authorization scheme along with a key
proof as described in Section 7.3 for the key bound to the access
token. For example, an access token bound using HTTP Message
Signatures would be sent as follows:
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GET /stuff HTTP/1.1
Host: resource.example.com
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=("@method" "@target-uri" "authorization")\
;created=1618884473;keyid="gnap-rsa";nonce="NAOEJF12ER2";tag="gnap"
Signature: sig1=:FQ+EjWqc38uLFByKa5y+c4WyYYwCTGUhidWKfr5L1Cha8FiPEw\
DxG7nWttpBLS/B6VLfkZJogPbclySs9MDIsAIJwHnzlcJjwXWR2lfvm2z3X7EkJHm\
Zp4SmyKOS34luAiKR1xwf32NYFolHmZf/SbHZJuWvQuS4U33C+BbsXz8MflFH1Dht\
H/C1E5i244gSbdLCPxzABc/Q0NHVSLo1qaouYIvnxXB8OT3K7mwWjsLh1GC5vFThb\
3XQ363r6f0OPRa4qWHhubR/d/J/lNOjbBdjq9AJ69oqNJ+A2XT+ZCrVasEJE0OBvD\
auQoiywhb8BMB7+PEINsPk5/8UvaNxbw==:
If the flags field contains the bearer flag, the access token is a
bearer token that MUST be sent using the Authorization Request Header
Field method defined in [RFC6750].
Authorization: Bearer OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
The Form-Encoded Body Parameter and URI Query Parameter methods of
[RFC6750] MUST NOT be used for GNAP access tokens.
7.3. Proving Possession of a Key with a Request
Any keys presented by the client instance to the AS or RS MUST be
validated as part of the request in which they are presented. The
type of binding used is indicated by the proof parameter of the key
object in Section 7.1. Key proof methods are specified either by a
string, which consists of the key proof method name on its own, or by
a JSON object with the required field method:
method: The name of the key proofing method to be used. REQUIRED.
Individual methods defined as objects MAY define additional
parameters as members in this object.
Values for the method defined by this specification are as follows:
"httpsig" (string or object): HTTP Signing signature headers. See
Section 7.3.1.
"mtls" (string): Mutual TLS certificate verification. See
Section 7.3.2.
"jwsd" (string): A detached JWS signature header. See
Section 7.3.3.
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"jws" (string): Attached JWS payload. See Section 7.3.4.
Additional proofing methods are defined by the GNAP Key Proofing
Methods Registry (Section 11.15).
Proof methods MAY be defined as both an object and a string. For
example, the httpsig method can be specified as an object with its
parameters explicitly declared, such as:
{
"proof": {
"method": "httpsig",
"alg": "ecdsa-p384-sha384",
"content-digest-alg": "sha-256"
}
}
The httpsig method also defines default behavior when it is passed as
a string form, using the signature algorithm specified by the
associated key material and the content digest is calculated using
sha-256. This configuration can be selected using the following
shortened form:
{
"proof": "httpsig"
}
All key binding methods used by this specification MUST cover all
relevant portions of the request, including anything that would
change the nature of the request, to allow for secure validation of
the request. Relevant aspects include the URI being called, the HTTP
method being used, any relevant HTTP headers and values, and the HTTP
message content itself. The verifier of the signed message MUST
validate all components of the signed message to ensure that nothing
has been tampered with or substituted in a way that would change the
nature of the request. Key binding method definitions MUST enumerate
how these requirements are fulfilled.
When a key proofing mechanism is bound to an access token, the key
being presented MUST be the key associated with the access token and
the access token MUST be covered by the signature method of the
proofing mechanism.
The key binding methods in this section MAY be used by other
components making calls as part of GNAP, such as the extensions
allowing the RS to make calls to the AS defined in
[I-D.ietf-gnap-resource-servers]. To facilitate this extended use,
the sections below are defined in generic terms of the "signer" and
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"verifier" of the HTTP message. In the core functions of GNAP
specified in this document, the "signer" is the client instance and
the "verifier" is the AS (for grant requests) or RS (for resource
requests), as appropriate.
When used for delegation in GNAP, these key binding mechanisms allow
the AS to ensure that the keys presented by the client instance in
the initial request are in control of the party calling any follow-up
or continuation requests. To facilitate this requirement, the
continuation response (Section 3.1) includes an access token bound to
the client instance's key (Section 2.3), and that key (or its most
recent rotation) MUST be proved in all continuation requests
(Section 5). Token management requests (Section 6) are similarly
bound to either the access token's own key or, in the case of bearer
tokens, the client instance's key.
In the following sections, unless otherwise noted, the RS256 JOSE
Signature Algorithm (defined in Section 3.3 of [RFC7518]) is applied
using the following RSA key (presented here in JWK format):
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NOTE: '\' line wrapping per RFC 8792
{
"kid": "gnap-rsa",
"p": "xS4-YbQ0SgrsmcA7xDzZKuVNxJe3pCYwdAe6efSy4hdDgF9-vhC5gjaRk\
i1wWuERSMW4Tv44l5HNrL-Bbj_nCJxr_HAOaesDiPn2PnywwEfg3Nv95Nn-\
eilhqXRaW-tJKEMjDHu_fmJBeemHNZI412gBnXdGzDVo22dvYoxd6GM",
"kty": "RSA",
"q": "rVdcT_uy-CD0GKVLGpEGRR7k4JO6Tktc8MEHkC6NIFXihk_6vAIOCzCD6\
LMovMinOYttpRndKoGTNdJfWlDFDScAs8C5n2y1STCQPRximBY-bw39-aZq\
JXMxOLyPjzuVgiTOCBIvLD6-8-mvFjXZk_eefD0at6mQ5qV3U1jZt88",
"d": "FHlhdTF0ozTliDxMBffT6aJVKZKmbbFJOVNten9c3lXKB3ux3NAb_D2dB\
7inp9EV23oWrDspFtvCvD9dZrXgRKMHofkEpo_SSvBZfgtH-OTkbY_TqtPF\
FLPKAw0JX5cFPnn4Q2xE4n-dQ7tpRCKl59vZLHBrHShr90zqzFp0AKXU5fj\
b1gC9LPwsFA2Fd7KXmI1drQQEVq9R-o18Pnn4BGQNQNjO_VkcJTiBmEIVT_\
KJRPdpVJAmbgnYWafL_hAfeb_dK8p85yurEVF8nCK5oO3EPrqB7IL4UqaEn\
5Sl3u0j8x5or-xrrAoNz-gdOv7ONfZY6NFoa-3f8q9wBAHUuQ",
"e": "AQAB",
"qi": "ogpNEkDKg22Rj9cDV_-PJBZaXMk66Fp557RT1tafIuqJRHEufSOYnsto\
bWPJ0gHxv1gVJw3gm-zYvV-wTMNgr2wVsBSezSJjPSjxWZtmT2z68W1DuvK\
kZy15vz7Jd85hmDlriGcXNCoFEUsGLWkpHH9RwPIzguUHWmTt8y0oXyI",
"dp": "dvCKGI2G7RLh3WyjoJ_Dr6hZ3LhXweB3YcY3qdD9BnxZ71mrLiMQg4c_\
EBnwqCETN_5sStn2cRc2JXnvLP3G8t7IFKHTT_i_TSTacJ7uT04MSa053Y3\
RfwbvLjRNPR0UKAE3ZxROUoIaVNuU_6-QMf8-2ilUv2GIOrCN87gP_Vk",
"alg": "RS256",
"dq": "iMZmELaKgT9_W_MRT-UfDWtTLeFjIGRW8aFeVmZk9R7Pnyt8rNzyN-IQ\
M40ql8u8J6vc2GmQGfokLlPQ6XLSCY68_xkTXrhoU1f-eDntkhP7L6XawSK\
Onv5F2H7wyBQ75HUmHTg8AK2B_vRlMyFKjXbVlzKf4kvqChSGEz4IjQ",
"n": "hYOJ-XOKISdMMShn_G4W9m20mT0VWtQBsmBBkI2cmRt4Ai8BfYdHsFzAt\
YKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8IkZ8NMwSrcUIBZGYX\
jHpwjzvfGvXH_5KJlnR3_uRUp4Z4Ujk2bCaKegDn11V2vxE41hqaPUnhRZx\
e0jRETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo-uv4BC0\
bunS0K3bA_3UgVp7zBlQFoFnLTO2uWp_muLEWGl67gBq9MO3brKXfGhi3kO\
zywzwPTuq-cVQDyEN7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQ"
}
Key proofing methods SHOULD define a mechanism to allow the rotation
of keys discussed in Section 6.1.1. Key rotation mechanisms MUST
define a way for presenting proof of two keys simultaneously with the
following attributes:
* The value of or reference to the new key material MUST be signed
by the existing key. Generally speaking, this amounts to using
the existing key to sign the content of the message which contains
the new key.
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* The signature of the old key MUST be signed by the new key.
Generally speaking, this means including the signature value of
the old key under the coverage of the new key.
7.3.1. HTTP Message Signatures
This method is indicated by the method value httpsig and can be
declared in either object form or string form.
When the proof method is specified in object form, the following
parameters are defined:
alg: The HTTP signature algorithm, from the HTTP Signature Algorithm
registry. REQUIRED.
content-digest-alg: The algorithm used for the Content-Digest field,
used to protect the content when present in the message.
REQUIRED.
This example uses the ECDSA signing algorithm over the P384 curve and
the SHA-512 hashing algorithm for the content digest.
{
"proof": {
"method": "httpsig",
"alg": "ecdsa-p384-sha384",
"content-digest-alg": "sha-512"
}
}
When the proof method is specified in string form, the signing
algorithm MUST be derived from the key material (such as using the
JWS algorithm in a JWK formatted key), and the content digest
algorithm MUST be sha-256.
{
"proof": "httpsig"
}
When using this method, the signer creates an HTTP Message Signature
as described in [I-D.ietf-httpbis-message-signatures]. The covered
components of the signature MUST include the following:
"@method": The method used in the HTTP request.
"@target-uri": The full request URI of the HTTP request.
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When the message contains request content, the covered components
MUST also include the following:
"content-digest": The Content-Digest header as defined in
[I-D.ietf-httpbis-digest-headers]. When the request message has
content, the signer MUST calculate this field value and include
the field in the request. The verifier MUST validate this field
value. REQUIRED when the message request contains message
content.
When the request is bound to an access token, the covered components
MUST also include the following:
"authorization": The Authorization header used to present the access
token as discussed in Section 7.2.
Other message components MAY also be included.
The signer MUST include the tag signature parameter with the value
gnap, and the verifier MUST verify that the parameter exists with
this value. The signer MUST include the created signature parameter
with a timestamp of when the signature was created, and the verifier
MUST ensure that the creation timestamp is sufficiently close to the
current time given expected network delay and clock skew. The signer
SHOULD include the nonce parameter with a unique and unguessable
value. When included, the verifier MUST determine that the nonce
value is unique within a reasonably short time period such as several
minutes.
If the signer's key presented is a JWK, the keyid parameter of the
signature MUST be set to the kid value of the JWK, the signing
algorithm used MUST be the JWS algorithm denoted by the key's alg
field of the JWK.
The explicit alg signature parameter MUST NOT be included in the
signature, since the algorithm will be derived either from the key
material or from the proof value.
In this example, the message content is the following JSON object:
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NOTE: '\' line wrapping per RFC 8792
{
"access_token": {
"access": [
"dolphin-metadata"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.foo/callback",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"key": {
"proof": "httpsig",
"jwk": {
"kid": "gnap-rsa",
"kty": "RSA",
"e": "AQAB",
"alg": "PS512",
"n": "hYOJ-XOKISdMMShn_G4W9m20mT0VWtQBsmBBkI2cmRt4Ai8Bf\
YdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8IkZ8NMwSrcUIBZG\
YXjHpwjzvfGvXH_5KJlnR3_uRUp4Z4Ujk2bCaKegDn11V2vxE41hqaPUnhRZxe0jR\
ETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo-uv4BC0bunS0K3bA_\
3UgVp7zBlQFoFnLTO2uWp_muLEWGl67gBq9MO3brKXfGhi3kOzywzwPTuq-cVQDyE\
N7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQ"
}
}
"display": {
"name": "My Client Display Name",
"uri": "https://client.foo/"
},
}
}
This content is hashed for the Content-Digest header using sha-256
into the following encoded value:
sha-256=:q2XBmzRDCREcS2nWo/6LYwYyjrlN1bRfv+HKLbeGAGg=:
The HTTP message signature input string is calculated to be the
following:
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NOTE: '\' line wrapping per RFC 8792
"@method": POST
"@target-uri": https://server.example.com/gnap
"content-digest": \
sha-256=:q2XBmzRDCREcS2nWo/6LYwYyjrlN1bRfv+HKLbeGAGg=:
"content-length": 988
"content-type": application/json
"@signature-params": ("@method" "@target-uri" "content-digest" \
"content-length" "content-type");created=1618884473\
;keyid="gnap-rsa";nonce="NAOEJF12ER2";tag="gnap"
This leads to the following full HTTP message request:
NOTE: '\' line wrapping per RFC 8792
POST /gnap HTTP/1.1
Host: server.example.com
Content-Type: application/json
Content-Length: 988
Content-Digest: sha-256=:q2XBmzRDCREcS2nWo/6LYwYyjrlN1bRfv+HKLbeGAG\
g=:
Signature-Input: sig1=("@method" "@target-uri" "content-digest" \
"content-length" "content-type");created=1618884473\
;keyid="gnap-rsa";nonce="NAOEJF12ER2";tag="gnap"
Signature: sig1=:c2uwTa6ok3iHZsaRKl1ediKlgd5cCAYztbym68XgX8gSOgK0Bt\
+zLJ19oGjSAHDjJxX2gXP2iR6lh9bLMTfPzbFVn4Eh+5UlceP+0Z5mES7v0R1+eHe\
OqBl0YlYKaSQ11YT7n+cwPnCSdv/6+62m5zwXEEftnBeA1ECorfTuPtau/yrTYEvD\
9A/JqR2h9VzAE17kSlSSsDHYA6ohsFqcRJavX29duPZDfYgkZa76u7hJ23yVxoUpu\
2J+7VUdedN/72N3u3/z2dC8vQXbzCPTOiLru12lb6vnBZoDbUGsRR/zHPauxhj9T+\
218o5+tgwYXw17othJSxIIOZ9PkIgz4g==:
{
"access_token": {
"access": [
"dolphin-metadata"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.foo/callback",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"key": {
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"proof": "httpsig",
"jwk": {
"kid": "gnap-rsa",
"kty": "RSA",
"e": "AQAB",
"alg": "PS512",
"n": "hYOJ-XOKISdMMShn_G4W9m20mT0VWtQBsmBBkI2cmRt4Ai8Bf\
YdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8IkZ8NMwSrcUIBZG\
YXjHpwjzvfGvXH_5KJlnR3_uRUp4Z4Ujk2bCaKegDn11V2vxE41hqaPUnhRZxe0jR\
ETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo-uv4BC0bunS0K3bA_\
3UgVp7zBlQFoFnLTO2uWp_muLEWGl67gBq9MO3brKXfGhi3kOzywzwPTuq-cVQDyE\
N7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQ"
}
}
"display": {
"name": "My Client Display Name",
"uri": "https://client.foo/"
},
}
}
The verifier MUST ensure that the signature covers all required
message components. If the HTTP Message includes content, the
verifier MUST calculate and verify the value of the Content-Digest
header. The verifier MUST validate the signature against the
expected key of the signer.
A received message MAY include multiple signatures, each with its own
label. The verifier MUST examine all included signatures until it
finds (at least) one that's acceptable according to its policy and
meets the requirements in this section.
7.3.1.1. Key Rotation using HTTP Message Signatures
When rotating a key using HTTP Message Signatures, the message, which
includes the new public key value or reference, is first signed with
the old key following all of the requirements in Section 7.3.1. The
message is then signed again with the new key by following all of the
requirements in Section 7.3.1 again with the following additional
requirements:
* The covered components MUST include the Signature and Signature-
Input values from the signature generated with the old key
* The tag value MUST be gnap-rotate
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For example, the following request to the token management endpoint
for rotating a token value contains the new key in the request. The
message is first signed using the old key and the resulting signature
is placed in "old-key":
NOTE: '\' line wrapping per RFC 8792
POST /token/PRY5NM33 HTTP/1.1
Host: server.example.com
Authorization: GNAP 4398.34-12-asvDa.a
Content-Digest: sha-512=:Fb/A5vnawhuuJ5xk2RjGrbbxr6cvinZqd4+JPY85u/\
JNyTlmRmCOtyVhZ1Oz/cSS4tsYen6fzpCwizy6UQxNBQ==:
Signature-Input: old-key=("@method" "@target-uri" "content-digest" \
"authorization");created=1618884475;keyid="test-key-ecc-p256"\
;tag="gnap"
Signature: old-key=:vN4IKYsJl2RLFe+tYEm4dHM4R4BToqx5D2FfH4ge5WOkgxo\
dI2QRrjB8rysvoSEGvAfiVJOWsGcPD1lU639Amw==:
{
"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-2",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
}
}
}
The signer then creates a new signature using the new key, adding the
signature input and value to the signature base.
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NOTE: '\' line wrapping per RFC 8792
"@method": POST
"@target-uri": https://server.example.com/token/PRY5NM33
"content-digest": sha-512=:Fb/A5vnawhuuJ5xk2RjGrbbxr6cvinZqd4+JPY85\
u/JNyTlmRmCOtyVhZ1Oz/cSS4tsYen6fzpCwizy6UQxNBQ==:
"authorization": GNAP 4398.34-12-asvDa.a
"signature";key="old-key": :YdDJjDn2Sq8FR82e5IcOLWmmf6wILoswlnRcz+n\
M+e8xjFDpWS2YmiMYDqUdri2UiJsZx63T1z7As9Kl6HTGkQ==:
"signature-input";key="old-key": ("@method" "@target-uri" \
"content-digest" "authorization");created=1618884475\
;keyid="test-key-ecc-p256";tag="gnap"
"@signature-params": ("@method" "@target-uri" "content-digest" \
"authorization" "signature";key="old-key" "signature-input"\
;key="old-key");created=1618884480;keyid="xyz-2"
;tag="gnap-rotate"
This signature is then added to the message:
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NOTE: '\' line wrapping per RFC 8792
POST /token/PRY5NM33 HTTP/1.1
Host: server.example.com
Authorization: GNAP 4398.34-12-asvDa.a
Content-Digest: sha-512=:Fb/A5vnawhuuJ5xk2RjGrbbxr6cvinZqd4+JPY85u/\
JNyTlmRmCOtyVhZ1Oz/cSS4tsYen6fzpCwizy6UQxNBQ==:
Signature-Input: old-key=("@method" "@target-uri" "content-digest" \
"authorization");created=1618884475;keyid="test-key-ecc-p256"\
;tag="gnap", \
new-key=("@method" "@target-uri" "content-digest" \
"authorization" "signature";key="old-key" "signature-input"\
;key="old-key");created=1618884480;keyid="xyz-2"
;tag="gnap-rotate"
Signature: old-key=:vN4IKYsJl2RLFe+tYEm4dHM4R4BToqx5D2FfH4ge5WOkgxo\
dI2QRrjB8rysvoSEGvAfiVJOWsGcPD1lU639Amw==:, \
new-key=:VWUExXQ0geWeTUKhCfDT7WJyT++OHSVbfPA1ukW0o7mmstdbvIz9iOuH\
DRFzRBm0MQPFVMpLDFXQdE3vi2SL3ZjzcX2qLwzAtyRB9+RsV2caAA80A5ZGMoo\
gUsKPk4FFDN7KRUZ0vT9Mo9ycx9Dq/996TOWtAmq5z0YUYEwwn+T6+NcW8rFtms\
s1ZfXG0EoAfV6ve25p+x40Y1rvDHsfkakTRB4J8jWVDybSe39tjIKQBo3uicDVw\
twewBMNidIa+66iF3pWj8w9RSb0cncEgvbkHgASqaZeXmxxG4gM8p1HH9v/OqQT\
Oggm5gTWmCQs4oxEmWsfTOxefunfh3X+Qw==:
{
"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-2",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
}
}
}
The verifier MUST validate both signatures before processing the
request for key rotation.
7.3.2. Mutual TLS
This method is indicated by the method value mtls in string form.
{
"proof": "mtls"
}
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The signer presents its TLS client certificate during TLS negotiation
with the verifier.
In this example, the certificate is communicated to the application
through the Client-Cert header field from a TLS reverse proxy as per
[RFC9440], leading to the following full HTTP request message:
POST /gnap HTTP/1.1
Host: server.example.com
Content-Type: application/jose
Content-Length: 1567
Client-Cert: \
:MIIC6jCCAdKgAwIBAgIGAXjw74xPMA0GCSqGSIb3DQEBCwUAMDYxNDAyBgNVBAMM\
K05JWU15QmpzRGp5QkM5UDUzN0Q2SVR6a3BEOE50UmppOXlhcEV6QzY2bVEwHhcN\
MjEwNDIwMjAxODU0WhcNMjIwMjE0MjAxODU0WjA2MTQwMgYDVQQDDCtOSVlNeUJq\
c0RqeUJDOVA1MzdENklUemtwRDhOdFJqaTl5YXBFekM2Nm1RMIIBIjANBgkqhkiG\
9w0BAQEFAAOCAQ8AMIIBCgKCAQEAhYOJ+XOKISdMMShn/G4W9m20mT0VWtQBsmBB\
kI2cmRt4Ai8BfYdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8I\
kZ8NMwSrcUIBZGYXjHpwjzvfGvXH/5KJlnR3/uRUp4Z4Ujk2bCaKegDn11V2vxE4\
1hqaPUnhRZxe0jRETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo+\
uv4BC0bunS0K3bA/3UgVp7zBlQFoFnLTO2uWp/muLEWGl67gBq9MO3brKXfGhi3k\
OzywzwPTuq+cVQDyEN7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQIDAQABMA0GCSqG\
SIb3DQEBCwUAA4IBAQBnYFK0eYHy+hVf2D58usj39lhL5znb/q9G35GBd/XsWfCE\
wHuLOSZSUmG71bZtrOcx0ptle9bp2kKl4HlSTTfbtpuG5onSa3swRNhtKtUy5NH9\
W/FLViKWfoPS3kwoEpC1XqKY6l7evoTCtS+kTQRSrCe4vbNprCAZRxz6z1nEeCgu\
NMk38yTRvx8ihZpVOuU+Ih+dOtVe/ex5IAPYxlQsvtfhsUZqc7IyCcy72WHnRHlU\
fn3pJm0S5270+Yls3Iv6h3oBAP19i906UjiUTNH3g0xMW+V4uLxgyckt4wD4Mlyv\
jnaQ7Z3sR6EsXMocAbXHIAJhwKdtU/fLgdwL5vtx:
{
"access_token": {
"access": [
"dolphin-metadata"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.foo/callback",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"key": {
"proof": "mtls",
"cert": "MIIC6jCCAdKgAwIBAgIGAXjw74xPMA0GCSqGSIb3DQEBCwUAMD\
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YxNDAyBgNVBAMMK05JWU15QmpzRGp5QkM5UDUzN0Q2SVR6a3BEOE50UmppOXlhcEV\
6QzY2bVEwHhcNMjEwNDIwMjAxODU0WhcNMjIwMjE0MjAxODU0WjA2MTQwMgYDVQQD\
DCtOSVlNeUJqc0RqeUJDOVA1MzdENklUemtwRDhOdFJqaTl5YXBFekM2Nm1RMIIBI\
jANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAhYOJ+XOKISdMMShn/G4W9m20mT\
0VWtQBsmBBkI2cmRt4Ai8BfYdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8\
KowlyVy8IkZ8NMwSrcUIBZGYXjHpwjzvfGvXH/5KJlnR3/uRUp4Z4Ujk2bCaKegDn\
11V2vxE41hqaPUnhRZxe0jRETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDad\
z8BkPo+uv4BC0bunS0K3bA/3UgVp7zBlQFoFnLTO2uWp/muLEWGl67gBq9MO3brKX\
fGhi3kOzywzwPTuq+cVQDyEN7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQIDAQABMA0\
GCSqGSIb3DQEBCwUAA4IBAQBnYFK0eYHy+hVf2D58usj39lhL5znb/q9G35GBd/Xs\
WfCEwHuLOSZSUmG71bZtrOcx0ptle9bp2kKl4HlSTTfbtpuG5onSa3swRNhtKtUy5\
NH9W/FLViKWfoPS3kwoEpC1XqKY6l7evoTCtS+kTQRSrCe4vbNprCAZRxz6z1nEeC\
guNMk38yTRvx8ihZpVOuU+Ih+dOtVe/ex5IAPYxlQsvtfhsUZqc7IyCcy72WHnRHl\
Ufn3pJm0S5270+Yls3Iv6h3oBAP19i906UjiUTNH3g0xMW+V4uLxgyckt4wD4Mlyv\
jnaQ7Z3sR6EsXMocAbXHIAJhwKdtU/fLgdwL5vtx"
}
"display": {
"name": "My Client Display Name",
"uri": "https://client.foo/"
},
},
"subject": {
"formats": ["iss_sub", "opaque"]
}
}
The verifier compares the TLS client certificate presented during
mutual TLS negotiation to the expected key of the signer. Since the
TLS connection covers the entire message, there are no additional
requirements to check.
Note that in many instances, the verifier will not do a full
certificate chain validation of the presented TLS client certificate,
as the means of trust for this certificate could be in something
other than a PKI system, such as a static registration or trust-on-
first-use. See Section 13.3 and Section 13.4 for some additional
considerations for this key proofing method.
7.3.2.1. Key Rotation using MTLS
Since it is not possible to present two client authenticated
certificates to a mutual TLS connection simultaneously, dynamic key
rotation for this proofing method is not defined. Instead, key
rotation for MTLS-based client instances is expected to be managed
through deployment practices, as discussed in Section 13.4.
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7.3.3. Detached JWS
This method is indicated by the method value jwsd in string form.
{
"proof": "jwsd"
}
The signer creates a JSON Web Signature (JWS) [RFC7515] object as
follows:
To protect the request, the JOSE header of the signature contains the
following claims:
kid (string): The key identifier. REQUIRED if the key is presented
in JWK format, this MUST be the value of the kid field of the key.
alg (string): The algorithm used to sign the request. MUST be
appropriate to the key presented. If the key is presented as a
JWK, this MUST be equal to the alg parameter of the key. MUST NOT
be none. REQUIRED.
typ (string): The type header, value "gnap-binding+jwsd". REQUIRED.
htm (string): The HTTP Method used to make this request, as a case-
sensitive ASCII string. Note that most public HTTP methods are in
uppercase ASCII by convention. REQUIRED.
uri (string): The HTTP URI used for this request. This value MUST
be an absolute URI, including all path and query components and no
fragment component. REQUIRED.
created (integer): A timestamp of when the signature was created, in
integer seconds since UNIX Epoch. REQUIRED.
When the request is bound to an access token, the JOSE header MUST
also include the following:
ath (string): The hash of the access token. The value MUST be the
result of Base64url encoding (with no padding) the SHA-256 digest
of the ASCII encoding of the associated access token's value.
REQUIRED.
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If the HTTP request has content, such as an HTTP POST or PUT method,
the payload of the JWS object is the Base64url encoding (without
padding) of the SHA256 digest of the bytes of the content. If the
request being made does not have content, such as an HTTP GET,
OPTIONS, or DELETE method, the JWS signature is calculated over an
empty payload.
The signer presents the signed object in compact form [RFC7515] in
the Detached-JWS HTTP Header field.
In this example, the JOSE Header contains the following parameters:
{
"alg": "RS256",
"kid": "gnap-rsa",
"uri": "https://server.example.com/gnap",
"htm": "POST",
"typ": "gnap-binding+jwsd",
"created": 1618884475
}
The request content is the following JSON object:
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NOTE: '\' line wrapping per RFC 8792
{
"access_token": {
"access": [
"dolphin-metadata"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.foo/callback",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"key": {
"proof": "jwsd",
"jwk": {
"kid": "gnap-rsa",
"kty": "RSA",
"e": "AQAB",
"alg": "RS256",
"n": "hYOJ-XOKISdMMShn_G4W9m20mT0VWtQBsmBBkI2cmRt4Ai8Bf\
YdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8IkZ8NMwSrcUIBZG\
YXjHpwjzvfGvXH_5KJlnR3_uRUp4Z4Ujk2bCaKegDn11V2vxE41hqaPUnhRZxe0jR\
ETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo-uv4BC0bunS0K3bA_\
3UgVp7zBlQFoFnLTO2uWp_muLEWGl67gBq9MO3brKXfGhi3kOzywzwPTuq-cVQDyE\
N7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQ"
}
}
"display": {
"name": "My Client Display Name",
"uri": "https://client.foo/"
},
}
}
This is hashed to the following Base64 encoded value:
PGiVuOZUcN1tRtUS6tx2b4cBgw9mPgXG3IPB3wY7ctc
This leads to the following full HTTP request message:
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NOTE: '\' line wrapping per RFC 8792
POST /gnap HTTP/1.1
Host: server.example.com
Content-Type: application/json
Content-Length: 983
Detached-JWS: eyJhbGciOiJSUzI1NiIsImNyZWF0ZWQiOjE2MTg4ODQ0NzUsImh0b\
SI6IlBPU1QiLCJraWQiOiJnbmFwLXJzYSIsInR5cCI6ImduYXAtYmluZGluZytqd3\
NkIiwidXJpIjoiaHR0cHM6Ly9zZXJ2ZXIuZXhhbXBsZS5jb20vZ25hcCJ9.PGiVuO\
ZUcN1tRtUS6tx2b4cBgw9mPgXG3IPB3wY7ctc.fUq-SV-A1iFN2MwCRW_yolVtT2_\
TZA2h5YeXUoi5F2Q2iToC0Tc4drYFOSHIX68knd68RUA7yHqCVP-ZQEd6aL32H69e\
9zuMiw6O_s4TBKB3vDOvwrhYtDH6fX2hP70cQoO-47OwbqP-ifkrvI3hVgMX9TfjV\
eKNwnhoNnw3vbu7SNKeqJEbbwZfpESaGepS52xNBlDNMYBQQXxM9OqKJaXffzLFEl\
-Xe0UnfolVtBraz3aPrPy1C6a4uT7wLda3PaTOVtgysxzii3oJWpuz0WP5kRujzDF\
wX_EOzW0jsjCSkL-PXaKSpZgEjNjKDMg9irSxUISt1C1T6q3SzRgfuQ
{
"access_token": {
"access": [
"dolphin-metadata"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.foo/callback",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"key": {
"proof": "jwsd",
"jwk": {
"kid": "gnap-rsa",
"kty": "RSA",
"e": "AQAB",
"alg": "RS256",
"n": "hYOJ-XOKISdMMShn_G4W9m20mT0VWtQBsmBBkI2cmRt4Ai8Bf\
YdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8IkZ8NMwSrcUIBZG\
YXjHpwjzvfGvXH_5KJlnR3_uRUp4Z4Ujk2bCaKegDn11V2vxE41hqaPUnhRZxe0jR\
ETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo-uv4BC0bunS0K3bA_\
3UgVp7zBlQFoFnLTO2uWp_muLEWGl67gBq9MO3brKXfGhi3kOzywzwPTuq-cVQDyE\
N7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQ"
}
}
"display": {
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"name": "My Client Display Name",
"uri": "https://client.foo/"
},
}
}
When the verifier receives the Detached-JWS header, it MUST parse and
validate the JWS object. The signature MUST be validated against the
expected key of the signer. If the HTTP message request contains
content, the verifier MUST calculate the hash of the content just as
the signer does, with no normalization or transformation of the
request. All required fields MUST be present and their values MUST
be valid. All fields MUST match the corresponding portions of the
HTTP message. For example, the htm field of the JWS header has to be
the same as the HTTP verb used in the request.
Note that this proof method depends on a specific cryptographic
algorithm, SHA-256, in two ways: the ath hash algorithm is hardcoded,
and computing the payload of the detached/attached signature also
uses a hardcoded hash. A future version of this document may address
crypto-agility for both these uses by replacing ath with a new header
that upgrades the algorithm, and possibly defining a new JWS header
that indicates the HTTP content's hash method.
7.3.3.1. Key Rotation using Detached JWS
When rotating a key using Detached JWS, the message, which includes
the new public key value or reference, is first signed with the old
key as described above using a JWS object with typ header value
"gnap-binding-rotation+jwsd". The value of the JWS object is then
taken as the payload of a new JWS object, to be signed by the new key
using the parameters above.
The value of the new JWS object is sent in the Detached-JWS header.
7.3.4. Attached JWS
This method is indicated by the method value jws in string form.
{
"proof": "jws"
}
The signer creates a JWS [RFC7515] object as follows:
To protect the request, the JWS header contains the following claims.
kid (string): The key identifier. REQUIRED if the key is presented
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in JWK format, this MUST be the value of the kid field of the key.
alg (string): The algorithm used to sign the request. MUST be
appropriate to the key presented. If the key is presented as a
JWK, this MUST be equal to the alg parameter of the key. MUST NOT
be none. REQUIRED.
typ (string): The type header, value "gnap-binding+jwsd". REQUIRED.
htm (string): The HTTP Method used to make this request, as a case-
sensitive ASCII string. (Note that most public HTTP methods are
in uppercase.) REQUIRED.
uri (string): The HTTP URI used for this request, including all path
and query components and no fragment component. REQUIRED.
created (integer): A timestamp of when the signature was created, in
integer seconds since UNIX Epoch. REQUIRED.
When the request is bound to an access token, the JOSE header MUST
also include the following:
ath (string): The hash of the access token. The value MUST be the
result of Base64url encoding (with no padding) the SHA-256 digest
of the ASCII encoding of the associated access token's value.
REQUIRED.
If the HTTP request has content, such as an HTTP POST or PUT method,
the payload of the JWS object is the JSON serialized content of the
request, and the object is signed according to JWS and serialized
into compact form [RFC7515]. The signer presents the JWS as the
content of the request along with a content type of application/jose.
The verifier MUST extract the payload of the JWS and treat it as the
request content for further processing.
If the request being made does not have content, such as an HTTP GET,
OPTIONS, or DELETE method, the JWS signature is calculated over an
empty payload and passed in the Detached-JWS header as described in
Section 7.3.3.
In this example, the JOSE header contains the following parameters:
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{
"alg": "RS256",
"kid": "gnap-rsa",
"uri": "https://server.example.com/gnap",
"htm": "POST",
"typ": "gnap-binding+jwsd",
"created": 1618884475
}
The request content, used as the JWS Payload, is the following JSON
object:
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NOTE: '\' line wrapping per RFC 8792
{
"access_token": {
"access": [
"dolphin-metadata"
]
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.foo/callback",
"nonce": "VJLO6A4CAYLBXHTR0KRO"
}
},
"client": {
"key": {
"proof": "jws",
"jwk": {
"kid": "gnap-rsa",
"kty": "RSA",
"e": "AQAB",
"alg": "RS256",
"n": "hYOJ-XOKISdMMShn_G4W9m20mT0VWtQBsmBBkI2cmRt4Ai8Bf\
YdHsFzAtYKOjpBR1RpKpJmVKxIGNy0g6Z3ad2XYsh8KowlyVy8IkZ8NMwSrcUIBZG\
YXjHpwjzvfGvXH_5KJlnR3_uRUp4Z4Ujk2bCaKegDn11V2vxE41hqaPUnhRZxe0jR\
ETddzsE3mu1SK8dTCROjwUl14mUNo8iTrTm4n0qDadz8BkPo-uv4BC0bunS0K3bA_\
3UgVp7zBlQFoFnLTO2uWp_muLEWGl67gBq9MO3brKXfGhi3kOzywzwPTuq-cVQDyE\
N7aL0SxCb3Hc4IdqDaMg8qHUyObpPitDQ"
}
}
"display": {
"name": "My Client Display Name",
"uri": "https://client.foo/"
},
},
"subject": {
"formats": ["iss_sub", "opaque"]
}
}
This leads to the following full HTTP request message:
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NOTE: '\' line wrapping per RFC 8792
POST /gnap HTTP/1.1
Host: server.example.com
Content-Type: application/jose
Content-Length: 1047
eyJhbGciOiJSUzI1NiIsImNyZWF0ZWQiOjE2MTg4ODQ0NzUsImh0bSI6IlBPU1QiLCJ\
raWQiOiJnbmFwLXJzYSIsInR5cCI6ImduYXAtYmluZGluZytqd3NkIiwidXJpIjoiaH\
R0cHM6Ly9zZXJ2ZXIuZXhhbXBsZS5jb20vZ25hcCJ9.CnsKICAgICJhY2Nlc3NfdG9r\
ZW4iOiB7CiAgICAgICAgImFjY2VzcyI6IFsKICAgICAgICAgICAgImRvbHBoaW4tbWV\
0YWRhdGEiCiAgICAgICAgXQogICAgfSwKICAgICJpbnRlcmFjdCI6IHsKICAgICAgIC\
Aic3RhcnQiOiBbInJlZGlyZWN0Il0sCiAgICAgICAgImZpbmlzaCI6IHsKICAgICAgI\
CAgICAgIm1ldGhvZCI6ICJyZWRpcmVjdCIsCiAgICAgICAgICAgICJ1cmkiOiAiaHR0\
cHM6Ly9jbGllbnQuZm9vL2NhbGxiYWNrIiwKICAgICAgICAgICAgIm5vbmNlIjogIlZ\
KTE82QTRDQVlMQlhIVFIwS1JPIgogICAgICAgIH0KICAgIH0sCiAgICAiY2xpZW50Ij\
ogewogICAgICAicHJvb2YiOiAiandzIiwKICAgICAgImtleSI6IHsKICAgICAgICAia\
ndrIjogewogICAgICAgICAgICAia2lkIjogImduYXAtcnNhIiwKICAgICAgICAgICAg\
Imt0eSI6ICJSU0EiLAogICAgICAgICAgICAiZSI6ICJBUUFCIiwKICAgICAgICAgICA\
gImFsZyI6ICJSUzI1NiIsCiAgICAgICAgICAgICJuIjogImhZT0otWE9LSVNkTU1TaG\
5fRzRXOW0yMG1UMFZXdFFCc21CQmtJMmNtUnQ0QWk4QmZZZEhzRnpBdFlLT2pwQlIxU\
nBLcEptVkt4SUdOeTBnNlozYWQyWFlzaDhLb3dseVZ5OElrWjhOTXdTcmNVSUJaR1lY\
akhwd2p6dmZHdlhIXzVLSmxuUjNfdVJVcDRaNFVqazJiQ2FLZWdEbjExVjJ2eEU0MWh\
xYVBVbmhSWnhlMGpSRVRkZHpzRTNtdTFTSzhkVENST2p3VWwxNG1VTm84aVRyVG00bj\
BxRGFkejhCa1BvLXV2NEJDMGJ1blMwSzNiQV8zVWdWcDd6QmxRRm9GbkxUTzJ1V3Bfb\
XVMRVdHbDY3Z0JxOU1PM2JyS1hmR2hpM2tPenl3endQVHVxLWNWUUR5RU43YUwwU3hD\
YjNIYzRJZHFEYU1nOHFIVXlPYnBQaXREUSIKICAgICAgICB9CiAgICAgIH0KICAgICA\
gImRpc3BsYXkiOiB7CiAgICAgICAgIm5hbWUiOiAiTXkgQ2xpZW50IERpc3BsYXkgTm\
FtZSIsCiAgICAgICAgInVyaSI6ICJodHRwczovL2NsaWVudC5mb28vIgogICAgICB9L\
AogICAgfSwKICAgICJzdWJqZWN0IjogewogICAgICAgICJmb3JtYXRzIjogWyJpc3Nf\
c3ViIiwgIm9wYXF1ZSJdCiAgICB9Cn0K.MwNoVMQp5hVxI0mCs9LlOUdFtkDXaA1_eT\
vOXq7DOGrtDKH7q4vP2xUq3fH2jRAZqnobo0WdPP3eM3NH5QUjW8pa6_QpwdIWkK7r-\
u_52puE0lPBp7J4U2w4l9gIbg8iknsmWmXeY5F6wiGT8ptfuEYGgmloAJd9LIeNvD3U\
LW2h2dz1Pn2eDnbyvgB0Ugae0BoZB4f69fKWj8Z9wvTIjk1LZJN1PcL7_zT8Lrlic9a\
PyzT7Q9ovkd1s-4whE7TrnGUzFc5mgWUn_gsOpsP5mIIljoEEv-FqOW2RyNYulOZl0Q\
8EnnDHV_vPzrHlUarbGg4YffgtwkQhdK72-JOxYQ
When the verifier receives an attached JWS request, it MUST parse and
validate the JWS object. The signature MUST be validated against the
expected key of the signer. All required fields MUST be present and
their values MUST be valid. All fields MUST match the corresponding
portions of the HTTP message. For example, the htm field of the JWS
header has to be the same as the HTTP verb used in the request.
Note that this proof method depends on a specific cryptographic
algorithm, SHA-256, in two ways: the ath hash algorithm is hardcoded,
and computing the payload of the detached/attached signature also
uses a hardcoded hash. A future version of this document may address
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crypto-agility for both these uses by replacing ath with a new header
that upgrades the algorithm, and possibly defining a new header that
indicates the HTTP content's hash method.
7.3.4.1. Key Rotation using Attached JWS
When rotating a key using Attached JWS, the message, which includes
the new public key value or reference, is first signed with the old
key using a JWS object with typ header value "gnap-binding-
rotation+jwsd". The value of the JWS object is then taken as the
payload of a new JWS object, to be signed by the new key.
8. Resource Access Rights
GNAP provides a rich structure for describing the protected resources
hosted by RSs and accessed by client software. This structure is
used when the client instance requests an access token (Section 2.1)
and when an access token is returned (Section 3.2). GNAP's structure
is designed to be analogous to the OAuth 2.0 Rich Authorization
Request data structure defined in [RFC9396].
The root of this structure is a JSON array. The elements of the JSON
array represent rights of access that are associated with the access
token. Individual rights of access can be defined by the RS as
either an object or a string. The resulting access is the union of
all elements within the array.
The access associated with the access token is described using
objects that each contain multiple dimensions of access. Each object
contains a REQUIRED type property that determines the type of API
that the token is used for and the structure of the rest of the
object. There is no expected interoperability between different type
definitions.
type (string): The type of resource request as a string. This field
MAY define which other fields are allowed in the request object.
REQUIRED.
The value of the type field is under the control of the AS. This
field MUST be compared using an exact byte match of the string value
against known types by the AS. The AS MUST ensure that there is no
collision between different authorization data types that it
supports. The AS MUST NOT do any collation or normalization of data
types during comparison. It is RECOMMENDED that designers of
general-purpose APIs use a URI for this field to avoid collisions
between multiple API types protected by a single AS.
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While it is expected that many APIs will have their own properties,
this specification defines a set of common data fields that are
designed to be usable across different types of APIs. This
specification does not require the use of these common fields by an
API definition but, instead, provides them as reusable generic
components for API designers to make use of. The allowable values of
all fields are determined by the API being protected, as defined by a
particular type value.
actions (array of strings): The types of actions the client instance
will take at the RS as an array of strings. For example, a client
instance asking for a combination of "read" and "write" access.
locations (array of strings): The location of the RS as an array of
strings. These strings are typically URIs identifying the
location of the RS.
datatypes (array of strings): The kinds of data available to the
client instance at the RS's API as an array of strings. For
example, a client instance asking for access to raw "image" data
and "metadata" at a photograph API.
identifier (string): A string identifier indicating a specific
resource at the RS. For example, a patient identifier for a
medical API or a bank account number for a financial API.
privileges (array of strings): The types or levels of privilege
being requested at the resource. For example, a client instance
asking for administrative level access, or access when the
resource owner is no longer online.
The following non-normative example is describing three kinds of
access (read, write, delete) to each of two different locations and
two different data types (metadata, images) for a single access token
using the fictitious photo-api type definition.
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"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"delete"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
}
]
While the exact semantics of interpreting the fields of an access
request object is subject to the definition of the type, it is
expected that the access requested for each object in the array is
the cross-product of all fields of the object. That is to say, the
object represents a request for all actions listed to be used at all
locations listed for all possible datatypes listed within the object.
Assuming the request above was granted, the client instance could
assume that it would be able to do a read action against the images
on the first server as well as a delete action on the metadata of the
second server, or any other combination of these fields, using the
same access token.
To request a different combination of access, such as requesting one
of the possible actions against one of the possible locations and a
different choice of possible actions against a different one of the
possible locations, the client instance can include multiple separate
objects in the resources array. The total access rights for the
resulting access token is the union of all objects. The following
non-normative example uses the same fictitious photo-api type
definition to request a single access token with more specifically
targeted access rights by using two discrete objects within the
request.
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"access": [
{
"type": "photo-api",
"actions": [
"read"
],
"locations": [
"https://server.example.net/"
],
"datatypes": [
"images"
]
},
{
"type": "photo-api",
"actions": [
"write",
"delete"
],
"locations": [
"https://resource.local/other"
],
"datatypes": [
"metadata"
]
}
]
The access requested here is for read access to images on one server
while simultaneously requesting write and delete access for metadata
on a different server, but importantly without requesting write or
delete access to images on the first server.
It is anticipated that API designers will use a combination of common
fields defined in this specification as well as fields specific to
the API itself. The following non-normative example shows the use of
both common and API-specific fields as part of two different
fictitious API type values. The first access request includes the
actions, locations, and datatypes fields specified here as well as
the API-specific geolocation field. The second access request
includes the actions and identifier fields specified here as well as
the API-specific currency field.
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"access": [
{
"type": "photo-api",
"actions": [
"read",
"write"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
],
"geolocation": [
{ lat: -32.364, lng: 153.207 },
{ lat: -35.364, lng: 158.207 }
]
},
{
"type": "financial-transaction",
"actions": [
"withdraw"
],
"identifier": "account-14-32-32-3",
"currency": "USD"
}
]
If this request is approved, the resulting access token's access
rights will be the union of the requested types of access for each of
the two APIs, just as above.
8.1. Requesting Resources By Reference
Instead of sending an object describing the requested resource
(Section 8), access rights MAY be communicated as a string known to
the AS representing the access being requested. Just like access
rights communicated as an object, access rights communicated as
reference strings indicate a specific access at a protected resource.
In the following non-normative example, three distinct resource
access rights are being requested.
"access": [
"read", "dolphin-metadata", "some other thing"
]
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This value is opaque to the client instance and MAY be any valid JSON
string, and therefore could include spaces, unicode characters, and
properly escaped string sequences. However, in some situations the
value is intended to be seen and understood by the client software's
developer. In such cases, the API designer choosing any such human-
readable strings SHOULD take steps to ensure the string values are
not easily confused by a developer, such as by limiting the strings
to easily disambiguated characters.
This functionality is similar in practice to OAuth 2.0's scope
parameter [RFC6749], where a single string represents the set of
access rights requested by the client instance. As such, the
reference string could contain any valid OAuth 2.0 scope value as in
Appendix C.5. Note that the reference string here is not bound to
the same character restrictions as in OAuth 2.0's scope definition.
A single access array MAY include both object-type and string-type
resource items. In this non-normative example, the client instance
is requesting access to a photo-api and financial-transaction API
type as well as the reference values of read, dolphin-metadata, and
some other thing.
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"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"delete"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read",
"dolphin-metadata",
{
"type": "financial-transaction",
"actions": [
"withdraw"
],
"identifier": "account-14-32-32-3",
"currency": "USD"
},
"some other thing"
]
The requested access is the union of all elements of the array,
including both objects and reference strings.
In order to facilitate the use of both object and reference strings
to access the same kind of APIs, the API designer can define a clear
mapping between these forms. One possible approach for choosing
reference string values is to use the same value as the type
parameter from the fully-specified object, with the API defining a
set of default behaviors in this case. For example, an API
definition could declare the following string:
"access": [
"photo-api"
]
As being equivalent to the following fully-defined object:
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"access": [
{
"type": "photo-api",
"actions": [ "read", "write", "delete" ],
"datatypes": [ "metadata", "image" ]
}
]
The exact mechanisms for relating reference strings is up to the API
designer. These are enforced by the AS, and the details are out of
scope for this specification.
9. Discovery
By design, GNAP minimizes the need for any pre-flight discovery. To
begin a request, the client instance only needs to know the grant
endpoint of the AS (a single URI) and which keys it will use to sign
the request. Everything else can be negotiated dynamically in the
course of the protocol.
However, the AS can have limits on its allowed functionality. If the
client instance wants to optimize its calls to the AS before making a
request, it MAY send an HTTP OPTIONS request to the grant request
endpoint to retrieve the server's discovery information. The AS MUST
respond with a JSON document with Content-Type application/json
containing a single object with the following fields:
grant_request_endpoint (string): The location of the AS's grant
request endpoint. The location MUST be an absolute URL [RFC3986]
with a scheme component (which MUST be "https"), a host component,
and optionally, port, path and query components and no fragment
components. This URL MUST match the URL the client instance used
to make the discovery request. REQUIRED.
interaction_start_modes_supported (array of strings): A list of the
AS's interaction start methods. The values of this list
correspond to the possible values for the interaction start
section (Section 2.5.1) of the request and MUST be values from the
GNAP Interaction Start Modes Registry (Section 11.8). OPTIONAL.
interaction_finish_methods_supported (array of strings): A list of
the AS's interaction finish methods. The values of this list
correspond to the possible values for the method element of the
interaction finish section (Section 2.5.2) of the request and MUST
be values from the GNAP Interaction Finish Methods Registry
(Section 11.9). OPTIONAL.
key_proofs_supported (array of strings): A list of the AS's
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supported key proofing mechanisms. The values of this list
correspond to possible values of the proof field of the key
section (Section 7.1) of the request and MUST be values from the
GNAP Key Proofing Methods Registry (Section 11.15). OPTIONAL.
sub_id_formats_supported (array of strings): A list of the AS's
supported subject identifier formats. The values of this list
correspond to possible values of the subject identifier section
(Section 2.2) of the request and MUST be values from the Subject
Identifier Formats Registry established by
[I-D.ietf-secevent-subject-identifiers]. OPTIONAL.
assertion_formats_supported (array of strings): A list of the AS's
supported assertion formats. The values of this list correspond
to possible values of the subject assertion section (Section 2.2)
of the request and MUST be values from the GNAP Assertion Formats
Registry (Section 11.5). OPTIONAL.
key_rotation_supported (boolean): The boolean "true" indicates that
rotation of access token bound keys by the client (Section 6.1.1)
is supported by the AS. The absence of this field or a boolean
"false" value indicates that this feature is not supported.
The information returned from this method is for optimization
purposes only. The AS MAY deny any request, or any portion of a
request, even if it lists a capability as supported. For example, a
given client instance can be registered with the mtls key proofing
mechanism, but the AS also returns other proofing methods from the
discovery document, then the AS will still deny a request from that
client instance using a different proofing mechanism. Similarly, an
AS with key_rotation_supported set to "true" can still deny any
request for rotating any access token's key for a variety of reasons.
Additional fields can be defined the GNAP Authorization Server
Discovery Fields Registry (Section 11.17).
9.1. RS-first Method of AS Discovery
If the client instance calls an RS without an access token, or with
an invalid access token, the RS SHOULD be explicit about the fact
that GNAP needs to be used to access the resource by responding with
the WWW-Authenticate header field and a GNAP challenge.
In some situations, the client instance might want to know with which
specific AS it needs to negotiate for access to that RS. The RS MAY
additionally return the following OPTIONAL parameters:
as_uri: The URI of the grant endpoint of the GNAP AS. Used by the
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client instance to call the AS to request an access token.
referrer: The URI of the GNAP RS. Sent by the client instance in
the Referer header as part of the grant request.
access: An opaque access reference as defined in Section 8.1. MUST
be sufficient for at least the action the client instance was
attempting to take at the RS and MAY allow additional access
rights as well. Sent by the client as an access right in the
grant request.
The client instance SHOULD then use both the referrer and access
parameters in its access token request. The client instance MUST
check that the referrer parameter is equal to the URI of the RS using
the simple string comparison method in Section 6.2.1 of [RFC3986].
The means for the RS to determine the value for the access reference
are out of scope of this specification, but some dynamic methods are
discussed in [I-D.ietf-gnap-resource-servers].
When receiving the following response from the RS:
NOTE: '\' line wrapping per RFC 8792
WWW-Authenticate: \
GNAP as_uri=https://as.example/tx\
;access=FWWIKYBQ6U56NL1\
;referrer=https://rs.example
The client instance then makes a request to the as_uri as described
in Section 2, with the value of referrer passed as an HTTP Referer
header field and the access reference passed unchanged into the
access array in the access_token portion of the request. The client
instance MAY request additional resources and other information.
In this non-normative example, the client instance is requesting a
single access token using the opaque access reference FWWIKYBQ6U56NL1
received from the RS in addition to the dolphin-metadata that the
client instance has been configured with out of band.
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POST /tx HTTP/1.1
Host: as.example
Referer: https://rs.example/resource
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
{
"access_token": {
"access": [
"FWWIKYBQ6U56NL1",
"dolphin-metadata"
]
},
"client": "KHRS6X63AJ7C7C4AZ9AO"
}
The client instance includes the Referer header field as a way for
the AS to know that the process is initiated through a discovery
process at the RS.
If issued, the resulting access token would contain sufficient access
to be used at both referenced resources.
Security considerations, especially related to the potential of a
compromised RS (Section 13.37) redirecting the requests of an
otherwise properly authenticated client, need to be carefully
considered when allowing such a discovery process. This risk can be
mitigated by an alternative pre-registration process so that the
client knows which AS protects which RS. There are also privacy
considerations related to revealing which AS is protecting a given
resource, discussed in Section 14.4.1.
9.2. Dynamic grant endpoint discovery
Additional methods of discovering the appropriate grant endpoint for
a given application are outside the scope of this specification.
This limitation is intentional, as many applications rely on static
configuration between the client instance and AS, as is common in
OAuth 2.0. However, the dynamic nature of GNAP makes it a prime
candidate for other extensions defining methods for discovery of the
appropriate AS grant endpoint at runtime. Advanced use cases could
define contextual methods for contextually providing this endpoint to
the client instance securely. Furthermore, GNAP's design
intentionally requires the client instance to only know the grant
endpoint and not additional parameters, since other functions and
values can be disclosed and negotiated during the grant process.
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10. Acknowledgements
The editors would like to thank the feedback of the following
individuals for their reviews, implementations, and contributions:
Åke Axeland, Aaron Parecki, Adam Omar Oueidat, Andrii Deinega,
Annabelle Backman, Dick Hardt, Dmitri Zagidulin, Dmitry Barinov,
Fabien Imbault, Florian Helmschmidt, Francis Pouatcha, George
Fletcher, Haardik Haardik, Hamid Massaoud, Jacky Yuan, Joseph Heenan,
Justin Richer, Kathleen Moriarty, Leif Johansson, Mike Jones, Mike
Varley, Nat Sakimura, Takahiko Kawasaki, Takahiro Tsuchiya, Yaron
Sheffer.
The editors would also like to thank the GNAP working group design
team of Kathleen Moriarty, Fabien Imbault, Dick Hardt, Mike Jones,
and Justin Richer, who incorporated elements from the XAuth and XYZ
proposals to create the first version of this document.
In addition, the editors would like to thank Aaron Parecki and Mike
Jones for insights into how to integrate identity and authentication
systems into the core protocol, and Justin Richer and Dick Hardt for
the use cases, diagrams, and insights provided in the XYZ and XAuth
proposals that have been incorporated here. The editors would like
to especially thank Mike Varley and the team at SecureKey for
feedback and development of early versions of the XYZ protocol that
fed into this standards work.
Finally, the editors want to acknowledge the immense contributions of
Aaron Parecki to the content of this document. We thank him for his
insight, input, and hard work, without which GNAP would not have
grown to what it is.
11. IANA Considerations
IANA is requested to add values to existing registries and to create
16 registries for the Grant Negotiation and Authorization Protocol
and to populate those registries with initial values as described in
this section.
All use of value typing is based on [RFC8259] data types and MUST be
one of the following: number, object, string, boolean, or array.
When the type is array, the contents of the array MUST be specified,
as in "array of objects" when one subtype is allowed or "array of
strings/objects" when multiple simultaneous subtypes are allowed.
When the type is object, the structure of the object MUST be
specified in the definition. If a parameter is available in
different types, each type SHOULD be registered separately.
General guidance for extension parameters is found in Appendix E.
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11.1. HTTP Authentication Scheme Registration
This specification requests registration of the following scheme in
the "Hypertext Transfer Protocol (HTTP) Authentication Scheme
Registry" defined be Section 18.5 of [HTTP]:
* Authentication Scheme Name: GNAP
* Reference: Section 7.2 of RFC nnnn
11.2. GNAP Grant Request Parameters
This document defines a GNAP grant request, for which IANA is asked
to create and maintain a new registry titled "GNAP Grant Request
Parameters". Initial values for this registry are given in
Section 11.2.2. Future assignments and modifications to existing
assignment are to be made through the Specification Required
registration policy [RFC8126].
The Designated Expert (DE) is expected to ensure that all
registrations follow the template presented in Section 11.2.1. The
DE is expected to ensure that the request parameter's definition is
sufficiently orthogonal to existing functionality provided by
existing parameters. The DE is expected to ensure that registrations
for the same name with different types are sufficiently close in
functionality so as not to cause confusion for developers. The DE is
expected to ensure that the request parameter's definition specifies
the expected behavior of the AS in response to the request parameter
for each potential state of the grant request.
11.2.1. Registration Template
Name:
An identifier for the parameter.
Type:
The JSON type allowed for the value.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
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+==============+==================+===========================+
| Name | Type | Specification document(s) |
+==============+==================+===========================+
| access_token | object | Section 2.1.1 of RFC nnnn |
+--------------+------------------+---------------------------+
| access_token | array of objects | Section 2.1.2 of RFC nnnn |
+--------------+------------------+---------------------------+
| subject | object | Section 2.2 of RFC nnnn |
+--------------+------------------+---------------------------+
| client | object | Section 2.3 of RFC nnnn |
+--------------+------------------+---------------------------+
| client | string | Section 2.3.1 of RFC nnnn |
+--------------+------------------+---------------------------+
| user | object | Section 2.4 of RFC nnnn |
+--------------+------------------+---------------------------+
| user | string | Section 2.4.1 of RFC nnnn |
+--------------+------------------+---------------------------+
| interact | object | Section 2.5 of RFC nnnn |
+--------------+------------------+---------------------------+
| interact_ref | string | Section 5.1 of RFC nnnn |
+--------------+------------------+---------------------------+
Table 1
11.3. GNAP Access Token Flags
This document defines a GNAP access token flags, for which IANA is
asked to create and maintain a new registry titled "GNAP Access Token
Flags". Initial values for this registry are given in
Section 11.3.2. Future assignments and modifications to existing
assignment are to be made through the Specification Required
registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.3.1. The DE is expected to ensure
that the flag specifies whether it applies to requests for tokens to
the AS, responses with tokens from the AS, or both.
11.3.1. Registration Template
Name:
An identifier for the parameter.
Allowed Use:
Where the flag is allowed to occur. Possible values are
"Request", "Response", and "Request, Response".
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Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
11.3.2. Initial Contents
+=========+===================+===========================+
| Name | Allowed Use | Specification document(s) |
+=========+===================+===========================+
| bearer | Request, Response | Section 2.1.1 and |
| | | Section 3.2.1 of RFC nnnn |
+---------+-------------------+---------------------------+
| durable | Response | Section 3.2.1 of RFC nnnn |
+---------+-------------------+---------------------------+
Table 2
11.4. GNAP Subject Information Request Fields
This document defines a means to request subject information from the
AS to the client instance, for which IANA is asked to create and
maintain a new registry titled "GNAP Subject Information Request
Fields". Initial values for this registry are given in
Section 11.4.2. Future assignments and modifications to existing
assignment are to be made through the Specification Required
registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.4.1. The DE is expected to ensure
that registrations for the same name with different types are
sufficiently close in functionality so as not to cause confusion for
developers.
11.4.1. Registration Template
Name:
An identifier for the parameter.
Type:
The JSON type allowed for the value.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
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+===================+==================+===========================+
| Name | Type | Specification document(s) |
+===================+==================+===========================+
| sub_id_formats | array of strings | Section 2.2 of RFC nnnn |
+-------------------+------------------+---------------------------+
| assertion_formats | array of strings | Section 2.2 of RFC nnnn |
+-------------------+------------------+---------------------------+
| sub_ids | array of objects | Section 2.2 of RFC nnnn |
+-------------------+------------------+---------------------------+
Table 3
11.5. GNAP Assertion Formats
This document defines a means to pass identity assertions between the
AS and client instance, for which IANA is asked to create and
maintain a new registry titled "GNAP Assertion Formats". Initial
values for this registry are given in Section 11.5.2. Future
assignments and modifications to existing assignment are to be made
through the Specification Required registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.5.1. The DE is expected to ensure
that the definition specifies the serialization format of the
assertion value as used within GNAP.
11.5.1. Registration Template
Name:
An identifier for the assertion format.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
11.5.2. Initial Contents
+==========+=========================================+
| Name | Specification document(s) |
+==========+=========================================+
| id_token | Section 2.2 and Section 3.4 of RFC nnnn |
+----------+-----------------------------------------+
| saml2 | Section 2.2 and Section 3.4 of RFC nnnn |
+----------+-----------------------------------------+
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Table 4
11.6. GNAP Client Instance Fields
This document defines a means to send information about the client
instance, for which IANA is asked to create and maintain a new
registry titled "GNAP Client Instance Fields". Initial values for
this registry are given in Section 11.6.2. Future assignments and
modifications to existing assignment are to be made through the
Specification Required registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.6.1. The DE is expected to ensure
that registrations for the same name with different types are
sufficiently close in functionality so as not to cause confusion for
developers.
11.6.1. Registration Template
Name:
An identifier for the parameter.
Type:
The JSON type allowed for the value.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
11.6.2. Initial Contents
+==========+========+===========================+
| Name | Type | Specification document(s) |
+==========+========+===========================+
| key | object | Section 7.1 of RFC nnnn |
+----------+--------+---------------------------+
| key | string | Section 7.1.1 of RFC nnnn |
+----------+--------+---------------------------+
| class_id | string | Section 2.3 of RFC nnnn |
+----------+--------+---------------------------+
| display | object | Section 2.3.2 of RFC nnnn |
+----------+--------+---------------------------+
Table 5
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11.7. GNAP Client Instance Display Fields
This document defines a means to send end-user facing displayable
information about the client instance, for which IANA is asked to
create and maintain a new registry titled "GNAP Client Instance
Display Fields". Initial values for this registry are given in
Section 11.7.2. Future assignments and modifications to existing
assignment are to be made through the Specification Required
registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.7.1. The DE is expected to ensure
that registrations for the same name with different types are
sufficiently close in functionality so as not to cause confusion for
developers.
11.7.1. Registration Template
Name:
An identifier for the parameter.
Type:
The JSON type allowed for the value.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
11.7.2. Initial Contents
+==========+========+===========================+
| Name | Type | Specification document(s) |
+==========+========+===========================+
| name | string | Section 2.3.2 of RFC nnnn |
+----------+--------+---------------------------+
| uri | string | Section 2.3.2 of RFC nnnn |
+----------+--------+---------------------------+
| logo_uri | string | Section 2.3.2 of RFC nnnn |
+----------+--------+---------------------------+
Table 6
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11.8. GNAP Interaction Start Modes
This document defines a means for the client instance to begin
interaction between the end-user and the AS, for which IANA is asked
to create and maintain a new registry titled "GNAP Interaction Start
Modes". Initial values for this registry are given in
Section 11.8.2. Future assignments and modifications to existing
assignment are to be made through the Specification Required
registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.8.1. The DE is expected to ensure
that registrations for the same name with different types are
sufficiently close in functionality so as not to cause confusion for
developers. The DE is expected to ensure that any registration using
an "object" type declares all additional parameters, their
optionality, and purpose. The DE is expected to ensure that the
start mode clearly defines what actions the client is expected to
take to begin interaction, what the expected user experience is, and
any security considerations for this communication from either party.
The DE is expected to ensure that the start mode documents
incompatibilities with other start modes or finish methods, if
applicable. The DE is expected to ensure that the start mode
provides enough information to uniquely identify the grant request
during the interaction. For example, tn the redirect and app modes,
this is done using a unique URI (including its parameters). In the
user_code and user_code_uri mode, this is done using the value of the
user code.
11.8.1. Registration Template
Mode:
An identifier for the interaction start mode.
Type:
The JSON type for the value, either "string" or "object", as
described in Section 2.5.1.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
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+===============+========+=============================+
| Mode | Type | Specification document(s) |
+===============+========+=============================+
| redirect | string | Section 2.5.1.1 of RFC nnnn |
+---------------+--------+-----------------------------+
| app | string | Section 2.5.1.2 of RFC nnnn |
+---------------+--------+-----------------------------+
| user_code | string | Section 2.5.1.3 of RFC nnnn |
+---------------+--------+-----------------------------+
| user_code_uri | string | Section 2.5.1.4 of RFC nnnn |
+---------------+--------+-----------------------------+
Table 7
11.9. GNAP Interaction Finish Methods
This document defines a means for the client instance to be notified
of the end of interaction between the end-user and the AS, for which
IANA is asked to create and maintain a new registry titled "GNAP
Interaction Finish Methods". Initial values for this registry are
given in Section 11.9.2. Future assignments and modifications to
existing assignment are to be made through the Specification Required
registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.9.1. The DE is expected to ensure
that all finish methods clearly define what actions the AS is
expected to take, what listening methods the client instance needs to
enable, and any security considerations for this communication from
either party. The DE is expected to ensure that all finish methods
document incompatibilities with any start modes, if applicable.
11.9.1. Registration Template
Method:
An identifier for the interaction finish method.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
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+==========+=============================+
| Mode | Specification document(s) |
+==========+=============================+
| redirect | Section 2.5.2.1 of RFC nnnn |
+----------+-----------------------------+
| push | Section 2.5.2.2 of RFC nnnn |
+----------+-----------------------------+
Table 8
11.10. GNAP Interaction Hints
This document defines a set of hints that a client instance can
provide to the AS to facilitate interaction with the end user, for
which IANA is asked to create and maintain a new registry titled
"GNAP Interaction Hints". Initial values for this registry are given
in Section 11.10.2. Future assignments and modifications to existing
assignment are to be made through the Specification Required
registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.10.1. The DE is expected to ensure
that all interaction hints clearly document the expected behaviors of
the AS in response to the hint, and that an AS not processing the
hint does not impede the operation of the AS or client instance.
11.10.1. Registration Template
Name:
An identifier for the parameter.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
11.10.2. Initial Contents
+============+===========================+
| Mode | Specification document(s) |
+============+===========================+
| ui_locales | Section 2.5.3 of RFC nnnn |
+------------+---------------------------+
Table 9
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11.11. GNAP Grant Response Parameters
This document defines a GNAP grant response, for which IANA is asked
to create and maintain a new registry titled "GNAP Grant Response
Parameters". Initial values for this registry are given in
Section 11.11.2. Future assignments and modifications to existing
assignment are to be made through the Specification Required
registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.11.1. The DE is expected to ensure
that the response parameter's definition is sufficiently orthogonal
to existing functionality provided by existing parameters. The DE is
expected to ensure that registrations for the same name with
different types are sufficiently close in functionality so as not to
cause confusion for developers. The DE is expected to ensure that
the response parameter's definition specifies grant states for which
the client instance can expect this parameter to appear in a response
message.
11.11.1. Registration Template
Name:
An identifier for the parameter.
Type:
The JSON type allowed for the value.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
11.11.2. Initial Contents
+=============+==================+===========================+
| Name | Type | Specification document(s) |
+=============+==================+===========================+
| continue | object | Section 3.1 of RFC nnnn |
+-------------+------------------+---------------------------+
| acces_token | object | Section 3.2.1 of RFC nnnn |
+-------------+------------------+---------------------------+
| acces_token | array of objects | Section 3.2.2 of RFC nnnn |
+-------------+------------------+---------------------------+
| interact | object | Section 3.3 of RFC nnnn |
+-------------+------------------+---------------------------+
| subject | object | Section 3.4 of RFC nnnn |
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+-------------+------------------+---------------------------+
| instance_id | string | Section 3.5 of RFC nnnn |
+-------------+------------------+---------------------------+
| error | object | Section 3.6 of RFC nnnn |
+-------------+------------------+---------------------------+
Table 10
11.12. GNAP Interaction Mode Responses
This document defines a means for the AS to provide to the client
instance information that is required to complete a particular
interaction mode, for which IANA is asked to create and maintain a
new registry titled "GNAP Interaction Mode Responses". Initial
values for this registry are given in Section 11.12.2. Future
assignments and modifications to existing assignment are to be made
through the Specification Required registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.12.1. If the name of the
registration matches the name of an interaction start mode, the DE is
expected to ensure that the response parameter is unambiguously
associated with the interaction start mode of the same name.
11.12.1. Registration Template
Name:
An identifier for the parameter.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
11.12.2. Initial Contents
+===============+===========================+
| Name | Specification document(s) |
+===============+===========================+
| redirect | Section 3.3 of RFC nnnn |
+---------------+---------------------------+
| app | Section 3.3 of RFC nnnn |
+---------------+---------------------------+
| user_code | Section 3.3 of RFC nnnn |
+---------------+---------------------------+
| user_code_uri | Section 3.3 of RFC nnnn |
+---------------+---------------------------+
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| finish | Section 3.3 of RFC nnnn |
+---------------+---------------------------+
| expires_in | Section 3.3 of RFC nnnn |
+---------------+---------------------------+
Table 11
11.13. GNAP Subject Information Response Fields
This document defines a means to return subject information from the
AS to the client instance, for which IANA is asked to create and
maintain a new registry titled "GNAP Subject Information Response
Fields". Initial values for this registry are given in
Section 11.13.2. Future assignments and modifications to existing
assignment are to be made through the Specification Required
registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.13.1. The DE is expected to ensure
that registrations for the same name with different types are
sufficiently close in functionality so as not to cause confusion for
developers.
11.13.1. Registration Template
Name:
An identifier for the parameter.
Type:
The JSON type allowed for the value.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
11.13.2. Initial Contents
+============+==================+===========================+
| Name | Type | Specification document(s) |
+============+==================+===========================+
| sub_ids | array of objects | Section 3.4 of RFC nnnn |
+------------+------------------+---------------------------+
| assertions | array of objects | Section 3.4 of RFC nnnn |
+------------+------------------+---------------------------+
| updated_at | string | Section 3.4 of RFC nnnn |
+------------+------------------+---------------------------+
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Table 12
11.14. GNAP Error Codes
This document defines a set of errors that the AS can return to the
client instance, for which IANA is asked to create and maintain a new
registry titled "GNAP Error Codes". Initial values for this registry
are given in Section 11.14.2. Future assignments and modifications
to existing assignment are to be made through the Specification
Required registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.14.1. The DE is expected to ensure
that the error response is sufficiently unique from other errors to
provide actionable information to the client instance. The DE is
expected to ensure that the definition of the error response
specifies all conditions in which the error response is returned, and
what the client instance's expected action is.
11.14.1. Registration Template
Error:
A unique string code for the error.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
11.14.2. Initial Contents
+============================+===========================+
| Error | Specification document(s) |
+============================+===========================+
| invalid_request | Section 3.6 of RFC nnnn |
+----------------------------+---------------------------+
| invalid_client | Section 3.6 of RFC nnnn |
+----------------------------+---------------------------+
| invalid_interaction | Section 3.6 of RFC nnnn |
+----------------------------+---------------------------+
| invalid_flag | Section 3.6 of RFC nnnn |
+----------------------------+---------------------------+
| invalid_rotation | Section 3.6 of RFC nnnn |
+----------------------------+---------------------------+
| key_rotation_not_supported | Section 3.6 of RFC nnnn |
+----------------------------+---------------------------+
| invalid_continuation | Section 3.6 of RFC nnnn |
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+----------------------------+---------------------------+
| user_denied | Section 3.6 of RFC nnnn |
+----------------------------+---------------------------+
| request_denied | Section 3.6 of RFC nnnn |
+----------------------------+---------------------------+
| unknown_interaction | Section 3.6 of RFC nnnn |
+----------------------------+---------------------------+
| too_fast | Section 3.6 of RFC nnnn |
+----------------------------+---------------------------+
| too_many_attempts | Section 3.6 of RFC nnnn |
+----------------------------+---------------------------+
Table 13
11.15. GNAP Key Proofing Methods
This document defines methods that the client instance can use to
prove possession of a key, for which IANA is asked to create and
maintain a new registry titled "GNAP Key Proofing Methods". Initial
values for this registry are given in Section 11.15.2. Future
assignments and modifications to existing assignment are to be made
through the Specification Required registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.15.1. The DE is expected to ensure
that registrations for the same name with different types are
sufficiently close in functionality so as not to cause confusion for
developers. The DE is expected to ensure that the proofing method
provides sufficient coverage of and binding to the protocol messages
to which it is applied. The DE is expected to ensure that the
proofing method definition clearly enumerates how all requirements in
Section 7.3 are fulfilled by the definition.
11.15.1. Registration Template
Method:
A unique string code for the key proofing method.
Type:
The JSON type allowed for the value.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
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+=========+========+===========================+
| Method | Type | Specification document(s) |
+=========+========+===========================+
| httpsig | string | Section 7.3.1 of RFC nnnn |
+---------+--------+---------------------------+
| httpsig | object | Section 7.3.1 of RFC nnnn |
+---------+--------+---------------------------+
| mtls | string | Section 7.3.2 of RFC nnnn |
+---------+--------+---------------------------+
| jwsd | string | Section 7.3.3 of RFC nnnn |
+---------+--------+---------------------------+
| jws | string | Section 7.3.4 of RFC nnnn |
+---------+--------+---------------------------+
Table 14
11.16. GNAP Key Formats
This document defines formats for a public key value, for which IANA
is asked to create and maintain a new registry titled "GNAP Key
Formats". Initial values for this registry are given in
Section 11.16.2. Future assignments and modifications to existing
assignment are to be made through the Specification Required
registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.16.1. The DE is expected to ensure
the key format specifies the structure and serialization of the key
material.
11.16.1. Registration Template
Format:
A unique string code for the key format.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
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+===========+===========================+
| Format | Specification document(s) |
+===========+===========================+
| jwk | Section 7.1 of RFC nnnn |
+-----------+---------------------------+
| cert | Section 7.1 of RFC nnnn |
+-----------+---------------------------+
| cert#S256 | Section 7.1 of RFC nnnn |
+-----------+---------------------------+
Table 15
11.17. GNAP Authorization Server Discovery Fields
This document defines a discovery document for an AS, for which IANA
is asked to create and maintain a new registry titled "GNAP
Authorization Server Discovery Fields". Initial values for this
registry are given in Section 11.17.2. Future assignments and
modifications to existing assignment are to be made through the
Specification Required registration policy [RFC8126].
The DE is expected to ensure that all registrations follow the
template presented in Section 11.17.1. The DE is expected to ensure
that registrations for the same name with different types are
sufficiently close in functionality so as not to cause confusion for
developers. The DE is expected to ensure that the values in the
discovery document are sufficient to provide optimization and hints
to the client instance, but that knowledge of the discovered value is
not required for starting a transaction with the AS.
11.17.1. Registration Template
Name:
An identifier for the parameter.
Type:
The JSON type allowed for the value.
Specification document(s):
Reference to the document(s) that specify the value, preferably
including a URI that can be used to retrieve a copy of the
document(s). An indication of the relevant sections may also be
included but is not required.
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+======================================+==========+===============+
| Name | Type | Specification |
| | | document(s) |
+======================================+==========+===============+
| grant_request_endpoint | string | Section 9 of |
| | | RFC nnnn |
+--------------------------------------+----------+---------------+
| interaction_start_modes_supported | array of | Section 9 of |
| | strings | RFC nnnn |
+--------------------------------------+----------+---------------+
| interaction_finish_methods_supported | array of | Section 9 of |
| | strings | RFC nnnn |
+--------------------------------------+----------+---------------+
| key_proofs_supported | array of | Section 9 of |
| | strings | RFC nnnn |
+--------------------------------------+----------+---------------+
| sub_id_formats_supported | array of | Section 9 of |
| | strings | RFC nnnn |
+--------------------------------------+----------+---------------+
| assertion_formats_supported | array of | Section 9 of |
| | strings | RFC nnnn |
+--------------------------------------+----------+---------------+
| key_rotation_supported | boolean | Section 9 of |
| | | RFC nnnn |
+--------------------------------------+----------+---------------+
Table 16
12. Implementation Status
Note: To be removed by RFC editor before publication.
*GNAP Authorization Service in Rust* implementation by David Skyberg.
https://github.com/dskyberg/gnap (https://github.com/dskyberg/gnap)
Prototype implementation of AS and client in Rust. MIT license.
*GNAP JS Client* from Interop Alliance, implementation by Dmitri
Zagidulin. https://github.com/interop-alliance/gnap-client-js
(https://github.com/interop-alliance/gnap-client-js) Prototype
implementation of client in JavaScript. MIT License.
*Rafiki* from Interledger Foundation. https://github.com/interledger/
rafiki (https://github.com/interledger/rafiki) Production
implementation of AS in JavaScript. Apache 2.0 license.
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*Sample GNAP Client in PHP* implementation by Aaron Parecki.
https://github.com/aaronpk/gnap-client-php
(https://github.com/aaronpk/gnap-client-php) Prototype implementation
of web application client and CLI client in PHP, with common support
library. CC0 license.
*SUNET Auth Server* from SUNET. https://github.com/SUNET/sunet-auth-
server (https://github.com/SUNET/sunet-auth-server) Production
implementation of AS in Python. BSD license.
*Trustbloc* from Gen Digital.
https://github.com/trustbloc/docs/blob/main/readthedocs/designs/
auth.md
(https://github.com/trustbloc/docs/blob/main/readthedocs/designs/
auth.md) Production implementation of AS and client in Go. Apache
2.0 license.
*Verified.ME* from SecureKey. https://verified.me/
(https://verified.me/) Production implementation of AS, client and
RS. Proprietary license.
*XYZ* from Bespoke Engineering, implementation by Justin Richer.
https://github.com/bspk/oauth.xyz-java (https://github.com/bspk/
oauth.xyz-java) Advanced prototype implementation of AS, client, and
RS in Java, with common support library. Prototype implementation of
SPA client in JavaScript. Apache 2.0 license.
13. Security Considerations
In addition to the normative requirements in this document,
implementors are strongly encouraged to consider these additional
security considerations in implementations and deployments of GNAP.
13.1. TLS Protection in Transit
All requests in GNAP made over untrusted network connections have to
be made over TLS as outlined in [BCP195] to protect the contents of
the request and response from manipulation and interception by an
attacker. This includes all requests from a client instance to the
AS, all requests from the client instance to an RS, and any requests
back to a client instance such as the push-based interaction finish
method. Additionally, all requests between a browser and other
components, such as during redirect-based interaction, need to be
made over TLS or use equivalent protection such as a network
connection local to the browser ("localhost").
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Even though requests from the client instance to the AS are signed,
the signature method alone does not protect the request from
interception by an attacker. TLS protects the response as well as
the request, preventing an attacker from intercepting requested
information as it is returned. This is particularly important in the
core protocol for security artifacts such as nonces and for personal
information such as subject information.
The use of key-bound access tokens does not negate the requirement
for protecting calls to the RS with TLS. While the keys and
signatures associated a bound access token will prevent an attacker
from using a stolen token, without TLS an attacker would be able to
watch the data being sent to the RS and returned from the RS during
legitimate use of the client instance under attack. Additionally,
without TLS an attacker would be able to profile the calls made
between the client instance and RS, possibly gaining information
about the functioning of the API between the client software and RS
software that would be otherwise unknown to the attacker.
Note that connections from the end user and RO's browser also need to
be be protected with TLS. This applies during initial redirects to
an AS's components during interaction, during any interaction with
the resource owner, and during any redirect back to the client
instance. Without TLS protection on these portions of the process,
an attacker could wait for a valid request to start and then take
over the resource owner's interaction session.
13.2. Signing Requests from the Client Software
Even though all requests in GNAP need to be transmitted over TLS or
its equivalent, the use of TLS alone is not sufficient to protect all
parts of a multi-party and multi-stage protocol like GNAP, and TLS is
not targeted at tying multiple requests to each other over time. To
account for this, GNAP makes use of message-level protection and key
presentation mechanisms that strongly associate a request with a key
held by the client instance (see Section 7).
During the initial request from a client instance to the AS, the
client instance has to identify and prove possession of a
cryptographic key. If the key is known to the AS, such as if it is
previously registered or dereferenceable to a trusted source, the AS
can associate a set of policies to the client instance identified by
the key. Without the requirement that the client instance prove that
it holds that key, the AS could not trust that the connection came
from any particular client and could not apply any associated
policies.
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Even more importantly, the client instance proving possession of a
key on the first request allows the AS to associate future requests
with each other by binding all future requests in that transaction to
the same key. The access token used for grant continuation is bound
to the same key and proofing mechanism used by the client instance in
its initial request, which means that the client instance needs to
prove possession of that same key in future requests allowing the AS
to be sure that the same client instance is executing the follow-ups
for a given ongoing grant request. Therefore, the AS has to ensure
that all subsequent requests for a grant are associated with the same
key that started the grant, or the most recent rotation of that key.
This need holds true even if the initial key is previously unknown to
the AS, such as would be the case when a client instance creates an
ephemeral key for its request. Without this ongoing association, an
attacker would be able to impersonate a client instance in the midst
of a grant request, potentially stealing access tokens and subject
information with impunity.
Additionally, all access tokens in GNAP default to be associated with
the key that was presented during the grant request that created the
access token. This association allows an RS to know that the
presenter of the access token is the same party that the token was
issued to, as identified by their keys. While non-bound bearer
tokens are an option in GNAP, these types of tokens have their own
tradeoffs discussed in Section 13.9.
TLS functions at the transport layer, ensuring that only the parties
on either end of that connection can read the information passed
along that connection. Each time a new connection is made, such as
for a new HTTP request, a new trust is re-established that is mostly
unrelated to previous connections. While modern TLS does make use of
session resumption, this still needs to be augmented with
authentication methods to determine the identity of parties on the
connections. In other words, it is not possible with TLS alone to
know that the same party is making a set of calls over time, since
each time a new TLS connection is established, both the client and
the server (or the server only when using Section 7.3.2) have to
validate the other party's identity. Such a verification can be
achieved via methods described in [I-D.ietf-uta-rfc6125bis], but
these are not enough to establish the identity of the client instance
in many cases.
To counter this, GNAP defines a set of key binding methods in
Section 7.3 that allow authentication and proof of possession by the
caller, which is usually the client instance. These methods are
intended to be used in addition to TLS on all connections.
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13.3. MTLS Message Integrity
The MTLS key proofing mechanism (Section 7.3.2) provides a means for
a client instance to present a key using a certificate at the TLS
layer. Since TLS protects the entire HTTP message in transit,
verification of the TLS client certificate presented with the message
provides a sufficient binding between the two. However, since TLS is
functioning at a separate layer from HTTP, there is no direct
connection between the TLS key presentation and the message itself,
other than the fact that the message was presented over the TLS
channel. That is to say, any HTTP message can be presented over the
TLS channel in question with the same level of trust. The verifier
is responsible for ensuring the key in the TLS client certificate is
the one expected for a particular request. For example, if the
request is a grant request (Section 2), the AS needs to compare the
TLS client certificate presented at the TLS layer to the key
identified in the request content itself (either by value or through
a referenced identifier).
Furthermore, the prevalence of the TLS-terminating reverse proxy
(TTRP) pattern in deployments adds a wrinkle to the situation. In
this common pattern, the TTRP validates the TLS connection and then
forwards the HTTP message contents onward to an internal system for
processing. The system processing the HTTP message no longer has
access to the original TLS connection's information and context. To
compensate for this, the TTRP could inject the TLS client certificate
into the forwarded request as a header parameter using [RFC9111],
giving the downstream system access to the certificate information.
The TTRP has to be trusted to provide accurate certificate
information, and the connection between the TTRP and the downstream
system also has to be protected. The TTRP could provide some
additional assurance, for example, by adding its own signature to the
Client-Cert header field using [I-D.ietf-httpbis-message-signatures].
This signature would be effectively ignored by GNAP (since it would
not use GNAP's tag parameter value) but would be understood by the
downstream service as part of its deployment.
Additional considerations for different types of deployment patterns
and key distribution mechanisms for MTLS are found in Section 13.4.
13.4. MTLS Deployment Patterns
GNAP does not specify how a client instance's keys could be made
known to the AS ahead of time. Public Key Infrastructure (PKI) can
be used to manage the keys used by client instances when calling the
AS, allowing the AS to trust a root key from a trusted authority.
This method is particularly relevant to the MTLS key proofing method,
where the client instance presents its certificate to the AS as part
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of the TLS connection. An AS using PKI to validate the MTLS
connection would need to ensure that the presented certificate was
issued by a trusted certificate authority before allowing the
connection to continue. PKI-based certificates would allow a key to
be revoked and rotated through management at the certificate
authority without requiring additional registration or management at
the AS. The PKI required to manage mutually-authenticated TLS has
historically been difficult to deploy, especially at scale, but it
remains an appropriate solution for systems where the required
management overhead is not an impediment.
MTLS in GNAP need not use a PKI backing, as self-signed certificates
and certificates from untrusted authorities can still be presented as
part of a TLS connection. In this case, the verifier would validate
the connection but accept whatever certificate was presented by the
client software. This specific certificate can then be bound to all
future connections from that client software by being bound to the
resulting access tokens, in a trust-on-first-use pattern. See
Section 13.3 for more considerations on MTLS as a key proofing
mechanism.
13.5. Protection of Client Instance Key Material
Client instances are identified by their unique keys, and anyone with
access to a client instance's key material will be able to
impersonate that client instance to all parties. This is true for
both calls to the AS as well as calls to an RS using an access token
bound to the client instance's unique key. As a consequence, it is
of utmost importance for a client instance to protect its private key
material.
Different types of client software have different methods for
creating, managing, and registering keys. GNAP explicitly allows for
ephemeral clients such as single-page applications (SPAs) and single-
user clients (such as mobile applications) to create and present
their own keys during the initial grant request without any explicit
pre-registration step. The client software can securely generate a
keypair on-device and present the public key, along with proof of
holding the associated private key, to the AS as part of the initial
request. To facilitate trust in these ephemeral keys, GNAP further
allows for an extensible set of client information to be passed with
the request. This information can include device posture and third-
party attestations of the client software's provenance and
authenticity, depending on the needs and capabilities of the client
software and its deployment.
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From GNAP's perspective, each distinct key is a different client
instance. However, multiple client instances can be grouped together
by an AS policy and treated similarly to each other. For instance,
if an AS knows of several different keys for different servers within
a cluster, the AS can decide that authorization of one of these
servers applies to all other servers within the cluster. An AS that
chooses to do this needs to be careful with how it groups different
client keys together in its policy, since the breach of one instance
would have direct effects on the others in the cluster.
Additionally, if an end user controls multiple instances of a single
type of client software, such as having an application installed on
multiple devices, each of these instances is expected to have a
separate key and be issued separate access tokens. However, if the
AS is able to group these separate instances together as described
above, it can streamline the authorization process for new instances
of the same client software. For example, if two client instances
can present proof of a valid installation of a piece of client
software, the AS would be able to associate the approval of the first
instance of this software to all related instances. The AS could
then choose to bypass an explicit prompt of the resource owner for
approval during authorization, since such approval has already been
given. An AS doing such a process would need to take assurance
measures that the different instances are in fact correlated and
authentic, as well as ensuring the expected resource owner is in
control of the client instance.
Finally, if multiple instances of client software each have the same
key, then from GNAP's perspective, these are functionally the same
client instance as GNAP has no reasonable way to differentiate
between them. This situation could happen if multiple instances
within a cluster can securely share secret information among
themselves. Even though there are multiple copies of the software,
the shared key makes these copies all present as a single instance.
It is considered bad practice to share keys between copies of
software unless they are very tightly integrated with each other and
can be closely managed. It is particularly bad practice to allow an
end user to copy keys between client instances and to willingly use
the same key in multiple instances.
13.6. Protection of Authorization Server
The AS performs critical functions in GNAP, including authenticating
client software, managing interactions with end users to gather
consent and provide notice, and issuing access tokens for client
instances to present to resource servers. As such, protecting the AS
is central to any GNAP deployment.
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If an attacker is able to gain control over an AS, they would be able
to create fraudulent tokens and manipulate registration information
to allow for malicious clients. These tokens and clients would be
trusted by other components in the ecosystem under the protection of
the AS.
If the AS is using signed access tokens, an attacker in control of
the AS's signing keys would be able to manufacture fraudulent tokens
for use at RS's under the protection of the AS.
If an attacker is able to impersonate an AS, they would be able to
trick legitimate client instances into making signed requests for
information which could potentially be proxied to a real AS. To
combat this, all communications to the AS need to be made over TLS or
its equivalent, and the software making the connection has to
validate the certificate chain of the host it is connecting to.
Consequently, protecting, monitoring, and auditing the AS is
paramount to preserving the security of a GNAP-protected ecosystem.
The AS presents attackers with a valuable target for attack.
Fortunately, the core focus and function of the AS is to provide
security for the ecosystem, unlike the RS whose focus is to provide
an API or the client software whose focus is to access the API.
13.7. Symmetric and Asymmetric Client Instance Keys
Many of the cryptographic methods used by GNAP for key-proofing can
support both asymmetric and symmetric cryptography, and can be
extended to use a wide variety of mechanisms. Implementers will find
useful the available guidelines on cryptographic key management
provided in [RFC4107]. While symmetric cryptographic systems have
some benefits in speed and simplicity, they have a distinct drawback
that both parties need access to the same key in order to do both
signing and verification of the message. When more than two parties
share the same symmetric key, data origin authentication is not
provided. Any party that knows the symmetric key can compute a valid
MAC; therefore, the contents could originate from any one of the
parties.
Use of symmetric cryptography means that when the client instance
calls the AS to request a token, the AS needs to know the exact value
of the client instance's key (or be able to derive it) in order to
validate the key proof signature. With asymmetric keys, the client
needs only to send its public key to the AS to allow for verification
that the client holds the associated private key, regardless of
whether that key was pre-registered or not with the AS.
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Symmetric keys also have the expected advantage of providing better
protection against quantum threats in the future. Also, these types
of keys (and their secure derivations) are widely supported among
many cloud-based key management systems.
When used to bind to an access token, a key value must be known by
the RS in order to validate the proof signature on the request.
Common methods for communicating these proofing keys include putting
information in a structured access token and allowing the RS to look
up the associated key material against the value of the access token.
With symmetric cryptography, both of these methods would expose the
signing key to the RS, and in the case of an structured access token,
potentially to any party that can see the access token itself unless
the token's payload has been encrypted. Any of these parties would
then be able to make calls using the access token by creating a valid
signature using the shared key. With asymmetric cryptography, the RS
needs to know only the public key associated with the token in order
to validate the request, and therefore the RS cannot create any new
signed calls.
While both signing approaches are allowed, GNAP treats these two
classes of keys somewhat differently. Only the public portion of
asymmetric keys are allowed to be sent by value in requests to the AS
when establishing a connection. Since sending a symmetric key (or
the private portion of an asymmetric key) would expose the signing
material to any parties on the request path, including any attackers,
sending these kinds of keys by value is prohibited. Symmetric keys
can still be used by client instances, but only if the client
instance can send a reference to the key and not its value. This
approach allows the AS to use pre-registered symmetric keys as well
as key derivation schemes to take advantage of symmetric cryptography
but without requiring key distribution at runtime, which would expose
the keys in transit.
Both the AS and client software can use systems such as hardware
security modules to strengthen their key security storage and
generation for both asymmetric and symmetric keys (see also
Section 7.1.2).
13.8. Generation of Access Tokens
The content of access tokens need to be such that only the generating
AS would be able to create them, and the contents cannot be
manipulated by an attacker to gain different or additional access
rights.
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One method for accomplishing this is to use a cryptographically
random value for the access token, generated by the AS using a secure
randomization function with sufficiently high entropy. The odds of
an attacker guessing the output of the randomization function to
collide with a valid access token are exceedingly small, and even
then the attacker would not have any control over what the access
token would represent since that information would be held close by
the AS.
Another method for accomplishing this is to use a structured token
that is cryptographically signed. In this case, the payload of the
access token declares to the RS what the token is good for, but the
signature applied by the AS during token generation covers this
payload. Only the AS can create such a signature and therefore only
the AS can create such a signed token. The odds of an attacker being
able to guess a signature value with a useful payload are exceedingly
small. This technique only works if all targeted RS's check the
signature of the access token. Any RS that does not validate the
signature of all presented tokens would be susceptible to injection
of a modified or falsified token. Furthermore, an AS has to
carefully protect the keys used to sign access tokens, since anyone
with access to these signing keys would be able to create seemingly-
valid access tokens using them.
13.9. Bearer Access Tokens
Bearer access tokens can be used by any party that has access to the
token itself, without any additional information. As a natural
consequence, any RS that a bearer token is presented to has the
technical capability of presenting that bearer token to another RS,
as long as the token is valid. It also means that any party that is
able capture of the token value in storage or in transit is able to
use the access token. While bearer tokens are inherently simpler,
this simplicity has been misapplied and abused in making needlessly
insecure systems. The downsides of bearer tokens have become more
pertinent lately as stronger authentication systems have caused some
attacks to shift to target tokens and APIs.
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In GNAP, key-bound access tokens are the default due to their higher
security properties. While bearer tokens can be used in GNAP, their
use should be limited to cases where the simplicity benefits outweigh
the significant security downsides. One common deployment pattern is
to use a gateway that takes in key-bound tokens on the outside, and
verifies the signatures on the incoming requests, but translates the
requests to a bearer token for use by trusted internal systems. The
bearer tokens are never issued or available outside of the internal
systems, greatly limiting the exposure of the less secure tokens but
allowing the internal deployment to benefit from the advantages of
bearer tokens.
13.10. Key-Bound Access Tokens
Key-bound access tokens, as the name suggests, are bound to a
specific key and must be presented along with proof of that key
during use. The key itself is not presented at the same time as the
token, so even if a token value is captured, it cannot be used to
make a new request. This is particularly true for an RS, which will
see the token value but will not see the keys used to make the
request (assuming asymmetric cryptography is in use, see
Section 13.7).
Key-bound access tokens provide this additional layer of protection
only when the RS checks the signature of the message presented with
the token. Acceptance of an invalid presentation signature, or
failure to check the signature entirely, would allow an attacker to
make calls with a captured access token without having access to the
related signing key material.
In addition to validating the signature of the presentation message
itself, the RS also needs to ensure that the signing key used is
appropriate for the presented token. If an RS does not ensure that
the right keys were used to sign a message with a specific token, an
attacker would be able to capture an access token and sign the
request with their own keys, thereby negating the benefits of using
key-bound access tokens.
The RS also needs to ensure that sufficient portions of the message
are covered by the signature. Any items outside the signature could
still affect the API's processing decisions, but these items would
not be strongly bound to the token presentation. As such, an
attacker could capture a valid request, then manipulate portions of
the request outside of the signature envelope in order to cause
unwanted actions at the protected API.
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Some key-bound tokens are susceptible to replay attacks, depending on
the details of the signing method used. Key proofing mechanisms used
with access tokens therefore need to use replay protection mechanisms
covered under the signature such as a per-message nonce, a reasonably
short time validity window, or other uniqueness constraints. The
details of using these will vary depending on the key proofing
mechanism in use, but for example, HTTP Message Signatures has both a
created and nonce signature parameter as well as the ability to cover
significant portions of the HTTP message. All of these can be used
to limit the attack surface.
13.11. Exposure of End-user Credentials to Client Instance
As a delegation protocol, one of the main goals of GNAP is to prevent
the client software from being exposed to any credentials or
information about the end user or resource owner as a requirement of
the delegation process. By using the variety of interaction
mechanisms, the resource owner can interact with the AS without ever
authenticating to the client software, and without the client
software having to impersonate the resource owner through replay of
their credentials.
Consequently, no interaction methods defined in the GNAP core require
the end user to enter their credentials, but it is technologically
possible for an extension to be defined to carry such values. Such
an extension would be dangerous as it would allow rogue client
software to directly collect, store, and replay the end user's
credentials outside of any legitimate use within a GNAP request.
The concerns of such an extension could be mitigated through use of a
challenge and response unlocked by the end user's credentials. For
example, the AS presents a challenge as part of an interaction start
method, and the client instance signs that challenge using a key
derived from a password presented by the end user. It would be
possible for the client software to collect this password in a secure
software enclave without exposing the password to the rest of the
client software or putting it across the wire to the AS. The AS can
validate this challenge response against a known password for the
identified end user. While an approach such as this does not remove
all of the concerns surrounding such a password-based scheme, it is
at least possible to implement in a more secure fashion than simply
collecting and replaying the password. Even so, such schemes should
only ever be used by trusted clients due to the ease of abusing them.
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13.12. Mixing Up Authorization Servers
If a client instance is able to work with multiple AS's
simultaneously, it is possible for an attacker to add a compromised
AS to the client instance's configuration and cause the client
software to start a request at the compromised AS. This AS could
then proxy the client's request to a valid AS in order to attempt to
get the resource owner to approve access for the legitimate client
instance.
A client instance needs to always be aware of which AS it is talking
to throughout a grant process, and ensure that any callback for one
AS does not get conflated with the callback to different AS. The
interaction finish hash calculation in Section 4.2.3 allows a client
instance to protect against this kind of substitution, but only if
the client instance validates the hash. If the client instance does
not use an interaction finish method or does not check the
interaction finish hash value, the compromised AS can be granted a
valid access token on behalf of the resource owner. See
[AXELAND2021] for details of one such attack, which has been since
addressed in this document by including the grant endpoint in the
interaction hash calculation. Note that the client instance still
needs to validate the hash for the attack to be prevented.
13.13. Processing of Client-Presented User Information
GNAP allows the client instance to present assertions and identifiers
of the current user to the AS as part of the initial request. This
information should only ever be taken by the AS as a hint, since the
AS has no way to tell if the represented person is present at the
client software, without using an interaction mechanism. This
information does not guarantee the given user is there, but it does
constitute a statement by the client software that the AS can take
into account.
For example, if a specific user is claimed to be present prior to
interaction, but a different user is shown to be present during
interaction, the AS can either determine this to be an error or
signal to the client instance through returned subject information
that the current user has changed from what the client instance
thought. This user information can also be used by the AS to
streamline the interaction process when the user is present. For
example, instead of having the user type in their account identifier
during interaction at a redirected URI, the AS can immediately
challenge the user for their account credentials. Alternatively, if
an existing session is detected, the AS can determine that it matches
the identifier provided by the client and subsequently skip an
explicit authentication event by the resource owner.
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In cases where the AS trusts the client software more completely, due
to policy or by previous approval of a given client instance, the AS
can take this user information as a statement that the user is
present and could issue access tokens and release subject information
without interaction. The AS should only take such action in very
limited circumstances, as a client instance could assert whatever it
likes for the user's identifiers in its request. The AS can limit
the possibility of this by issuing randomized opaque identifiers to
client instances to represent different end user accounts after an
initial login.
When a client instance presents an assertion to the AS, the AS needs
to evaluate that assertion. Since the AS is unlikely to be the
intended audience of an assertion held by the client software, the AS
will need to evaluate the assertion in a different context. Even in
this case, the AS can still evaluate that the assertion was generated
by a trusted party, was appropriately signed, and is within any time
validity windows stated by the assertion. If the client instance's
audience identifier is known to the AS and can be associated with the
client instance's presented key, the AS can also evaluate that the
appropriate client instance is presenting the claimed assertion. All
of this will prevent an attacker from presenting a manufactured
assertion, or one captured from an untrusted system. However,
without validating the audience of the assertion, a captured
assertion could be presented by the client instance to impersonate a
given end user. In such cases, the assertion offers little more
protection than a simple identifier would.
A special case exists where the AS is the generator of the assertion
being presented by the client instance. In these cases, the AS can
validate that it did issue the assertion and it is associated with
the client instance presenting the assertion.
13.14. Client Instance Pre-registration
Each client instance is identified by its own unique key, and for
some kinds of client software such as a web server or backend system,
this identification can be facilitated by registering a single key
for a piece of client software ahead of time. This registration can
be associated with a set of display attributes to be used during the
authorization process, identifying the client software to the user.
In these cases, it can be assumed that only one instance of client
software will exist, likely to serve many different users.
A client's registration record needs to include its identifying key.
Furthermore, it is the case that any clients using symmetric
cryptography for key proofing mechanisms need to have their keys pre-
registered. The registration should also include any information
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that would aid in the authorization process, such as a display name
and logo. The registration record can also limit a given client to
ask for certain kinds of information and access, or be limited to
specific interaction mechanisms at runtime.
It also is sensible to pre-register client instances when the
software is acting autonomously, without the need for a runtime
approval by a resource owner or any interaction with an end user. In
these cases, an AS needs to rest on the trust decisions that have
been determined prior to runtime in determining what rights and
tokens to grant to a given client instance.
However, it does not make sense to pre-register many types of
clients. Single-page applications (SPAs) and mobile/desktop
applications in particular present problems with pre-registration.
For SPAs, the instances are ephemeral in nature and long-term
registration of a single instance leads to significant storage and
management overhead at the AS. For mobile applications, each
installation of the client software is a separate instance, and
sharing a key among all instances would be detrimental to security as
the compromise of any single installation would compromise all copies
for all users.
An AS can treat these classes of client software differently from
each other, perhaps by allowing access to certain high-value APIs
only to pre-registered known clients, or by requiring an active end
user delegation of authority to any client software not pre-
registered.
An AS can also provide warnings and caveats to resource owners during
the authorization process, allowing the user to make an informed
decision regarding the software they are authorizing. For example,
if the AS has done vetting of the client software and this specific
instance, it can present a different authorization screen compared to
a client instance that is presenting all of its information at
runtime.
Finally, an AS can use platform attestations and other signals from
the client instance at runtime to determine whether the software
making the request is legitimate or not. The details of such
attestations are outside the scope of the core protocol, but the
client portion of a grant request provides a natural extension point
to such information through the Client Instance Fields registry
(Section 11.6).
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13.15. Client Instance Impersonation
If client instances are allowed to set their own user-facing display
information, such as a display name and website URL, a malicious
client instance could impersonate legitimate client software for the
purposes of tricking users into authorizing the malicious client.
Requiring clients to pre-register does not fully mitigate this
problem since many pre-registration systems have self-service portals
for management of client registration, allowing authenticated
developers to enter self-asserted information into the management
portal.
An AS can mitigate this by actively filtering all self-asserted
values presented by client software, both dynamically as part of GNAP
and through a registration portal, to limit the kinds of
impersonation that would be done.
An AS can also warn the resource owner about the provenance of the
information it is displaying, allowing the resource owner to make a
more informed delegation decision. For example, an AS can visually
differentiate between a client instance that can be traced back to a
specific developer's registration and an instance that has self-
asserted its own display information.
13.16. Client-Hosted Logo URI
The logo_uri client display field defined in Section 2.3.2 allows the
client instance to specify a URI from which an image can be fetched
for display during authorization decisions. When the URI points to
an externally hosted resource (as opposed to a data: URI), the
logo_uri field presents challenges in addition to the considerations
in Section 13.15.
When a logo_uri is externally hosted, the client software (or the
host of the asset) can change the contents of the logo without
informing the AS. Since the logo is considered an aspect of the
client software's identity, this flexibility allows for a more
dynamically-managed client instance that makes use of the distributed
systems.
However, this same flexibility allows the host of the asset to change
the hosted file in a malicious way, such as replacing the image
content with malicious software for download or imitating a different
piece of client software. Additionally, the act of fetching the URI
could accidentally leak information to the image host in the HTTP
Referer header field, if one is sent. Even though GNAP intentionally
does not include security parameters in front-channel URI's wherever
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possible, the AS still should take steps to ensure that this
information does not leak accidentally, such as setting a referrer
policy on image links or displaying images only from paged served
from a URI with no sensitive security or identity information.
To avoid these issues, the AS can insist on the use of data: URIs,
though that might not be practical for all types of client software.
Alternatively, the AS could pre-fetch the content of the URI and
present its own copy to the resource owner instead. This practice
opens the AS to potential SSRF attacks, as discussed in
Section 13.34.
13.17. Interception of Information in the Browser
Most information passed through the web-browser is susceptible to
interception and possible manipulation by elements within the browser
such as scripts loaded within pages. Information in the URI is
exposed through browser and server logs, and can also leak to other
parties through HTTP Referer headers.
GNAP's design limits the information passed directly through the
browser, allowing for opaque URIs in most circumstances. For the
redirect-based interaction finish mechanism, named query parameters
are used to carry unguessable opaque values. For these, GNAP
requires creation and validation of a cryptographic hash to protect
the query parameters added to the URI and associate them with an
ongoing grant process and values not passed in the URI. The client
instance has to properly validate this hash to prevent an attacker
from injecting an interaction reference intended for a different AS
or client instance.
Several interaction start mechanisms use URIs created by the AS and
passed to the client instance. While these URIs are opaque to the
client instance, it's possible for the AS to include parameters,
paths, and other pieces of information that could leak security data
or be manipulated by a party in the middle of the transaction. An AS
implementation can avoid this problem by creating URIs using
unguessable values that are randomized for each new grant request.
13.18. Callback URI Manipulation
The callback URI used in interaction finish mechanisms is defined by
the client instance. This URI is opaque to the AS, but can contain
information relevant to the client instance's operations. In
particular, the client instance can include state information to
allow the callback request to be associated with an ongoing grant
request.
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Since this URI is exposed to the end user's browser, it is
susceptible to both logging and manipulation in transit before the
request is made to the client software. As such, a client instance
should never put security-critical or private information into the
callback URI in a cleartext form. For example, if the client
software includes a post-redirect target URI in its callback URI to
the AS, this target URI could be manipulated by an attacker, creating
an open redirector at the client. Instead, a client instance can use
an unguessable identifier in the URI that can then be used by the
client software to look up the details of the pending request. Since
this approach requires some form of statefulness by the client
software during the redirection process, clients that are not capable
of holding state through a redirect should not use redirect-based
interaction mechanisms.
13.19. Redirection Status Codes
As already described in [I-D.ietf-oauth-security-topics], a server
should never use the HTTP 307 status code to redirect a request that
potentially contains user credentials. If an HTTP redirect is used
for such a request, the HTTP status code 303 "See Other" should be
used instead.
The status code 307, as defined in the HTTP standard [HTTP], requires
the user agent to preserve the method and content of a request, thus
submitting the content of the POST request to the redirect target.
In the HTTP standard [HTTP], only the status code 303 unambiguously
enforces rewriting the HTTP POST request to an HTTP GET request,
which eliminates the POST content from the redirected request. For
all other status codes, including status code 302, user agents are
allowed not to rewrite a POST request into a GET request and thus to
resubmit the contents.
The use of status code 307 results in a vulnerability when using the
redirect interaction finish method (Section 3.3.5). With this
method, the AS potentially prompts the RO to enter their credentials
in a form that is then submitted back to the AS (using an HTTP POST
request). The AS checks the credentials and, if successful, may
directly redirect the RO to the client instance's redirect URI. Due
to the use of status code 307, the RO's user agent now transmits the
RO's credentials to the client instance. A malicious client instance
can then use the obtained credentials to impersonate the RO at the
AS.
Redirection away from the initial URI in an interaction session could
also leak information found in that initial URI through the HTTP
Referer header field, which would be sent by the user agent to the
redirect target. To avoid such leakage, a server can first redirect
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to an internal interstitial page without any identifying or sensitive
information on the URI before processing the request. When the user
agent is ultimately redirected from this page, no part of the
original interaction URI will be found in the Referer header.
13.20. Interception of Responses from the AS
Responses from the AS contain information vital to both the security
and privacy operations of GNAP. This information includes nonces
used in cryptographic calculations, subject identifiers, assertions,
public keys, and information about what client software is requesting
and was granted.
In addition, if bearer tokens are used or keys are issued alongside a
bound access token, the response from the AS contains all information
necessary for use of the contained access token. Any party that is
capable of viewing such a response, such as an intermediary proxy,
would be able to exfiltrate and use this token. If the access token
is instead bound to the client instance's presented key,
intermediaries no longer have sufficient information to use the
token. They can still, however, gain information about the end user
as well as the actions of the client software.
13.21. Key Distribution
GNAP does not define ways for the client instances keys to be
provided to the client instances, particularly in light of how those
keys are made known to the AS. These keys could be generated
dynamically on the client software or pre-registered at the AS in a
static developer portal. The keys for client instances could also be
distributed as part of the deployment process of instances of the
client software. For example, an application installation framework
could generate a keypair for each copy of client software, then both
install it into the client software upon installation and registering
that instance with the AS.
Alternatively, it's possible for the AS to generate keys to be used
with access tokens that are separate from the keys used by the client
instance to request tokens. In this method, the AS would generate
the asymmetric keypair or symmetric key and return the public key or
key reference, to the client instance alongside the access token
itself. The means for the AS to return generated key values to the
client instance are out of scope, since GNAP does not allow the
transmission of private or shared key information within the protocol
itself.
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Additionally, if the token is bound to a key other than the client
instance's presented key, this opens a possible attack surface for an
attacker's AS to request an access token then substitute their own
key material in the response to the client instance. The attacker's
AS would need to be able to use the same key as the client instance,
but this setup would allow an attacker's AS to make use of a
compromised key within a system. This attack can be prevented by
only binding access tokens to the client instance's presented keys,
and by having client instances have a strong association between
which keys they expect to use and the AS they expect to use them on.
This attack is also only able to be propagated on client instances
that talk to more than one AS at runtime, which can be limited by the
client software.
13.22. Key Rotation Policy
When keys are rotated, there could be a delay in the propagation of
that rotation to various components in the AS's ecosystem. The AS
can define its own policy regarding the timeout of the previously-
bound key, either making it immediately obsolete or allowing for a
limited grace period during which both the previously-bound key and
the current key can be used for signing requests. Such a grace
period can be useful when there are multiple running copies of the
client that are coordinated with each other. For example, the client
software could be deployed as a cloud service with multiple
orchestrated nodes. Each of these copies is deployed using the same
key and therefore all the nodes represent the same client instance to
the AS. In such cases, it can be difficult, or even impossible, to
update the keys on all these copies in the same instant.
The need for accommodating such known delays in the system needs to
be balanced with the risk of allowing an old key to still be used.
Narrowly restricting the exposure opportunities for exploit at the AS
in terms of time, place, and method makes exploit significantly more
difficult, especially if the exception happens only once. For
example, the AS can reject requests from the previously-bound key (or
any previous one before it) to cause rotation to a new key, or at
least ensure that the rotation happens in an idempotent way to the
same new key.
See also the related considerations for token values in
Section 13.33.
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13.23. Interaction Finish Modes and Polling
During the interaction process, the client instance usually hands
control of the user experience over to another component, be it the
system browser, another application, or some action the resource
owner is instructed to take on another device. By using an
interaction finish method, the client instance can be securely
notified by the AS when the interaction is completed and the next
phase of the protocol should occur. This process includes
information that the client instance can use to validate the finish
call from the AS and prevent some injection, session hijacking, and
phishing attacks.
Some types of client deployment are unable to receive an interaction
finish message. Without an interaction finish method to notify it,
the client instance will need to poll the grant continuation API
while waiting for the resource owner to approve or deny the request.
An attacker could take advantage of this situation by capturing the
interaction start parameters and phishing a legitimate user into
authorizing the attacker's waiting client instance, which would in
turn have no way of associating the completed interaction from the
targeted user with the start of the request from the attacker.
However, it is important to note that this pattern is practically
indistinguishable from some legitimate use cases. For example, a
smart device emits a code for the resource owner to enter on a
separate device. The smart device has to poll because the expected
behavior is that the interaction will take place on the separate
device, without a way to return information to the original device's
context.
As such, developers need to weigh the risks of forgoing an
interaction finish method against the deployment capabilities of the
client software and its environment. Due to the increased security,
an interaction finish method should be employed whenever possible.
13.24. Session Management for Interaction Finish Methods
When using an interaction finish method such as redirect or push, the
client instance receives an unsolicited inbound request from an
unknown party over HTTPS. The client instance needs to be able to
successfully associate this incoming request with a specific pending
grant request being managed by the client instance. If the client
instance is not careful and precise about this, an attacker could
associate their own session at the client instance with a stolen
interaction response. The means of preventing this varies by the
type of client software and interaction methods in use. Some common
patterns are enumerated here.
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If the end user interacts with the client instance through a web
browser and the redirect interaction finish method is used, the
client instance can ensure that the incoming HTTP request from the
finish method is presented in the same browser session that the grant
request was started in. This technique is particularly useful when
the redirect interaction start mode is used as well, since in many
cases the end user will follow the redirection with the same browser
that they are using to interact with the client instance. The client
instance can then store the relevant pending grant information in the
session, either in the browser storage directly (such as with a
single-page application) or in an associated session store on a back-
end server. In both cases, when the incoming request reaches the
client instance, the session information can be used to ensure that
the same party that started the request is present as the request
finishes.
Ensuring that the same party that started a request is present when
that request finishes can prevent phishing attacks, where an attacker
starts a request at an honest client instance and tricks an honest RO
into authorizing it. For example, if an honest end user (that also
acts as the RO) wants to start a request through a client instance
controlled by the attacker, the attacker can start a request at an
honest client instance and then redirect the honest end user to the
interaction URI from the attackers session with the honest client
instance. If the honest end user then fails to realize that they are
not authorizing the attacker-controlled client instance (with which
it started its request) but instead the honest client instance when
interacting with the AS, the attacker's session with the honest
client instance would be authorized. This would give the attacker
access to the honest end user's resources that the honest client
instance is authorized to access. However, if after the interaction
the AS redirects the honest end user back to the client instance
whose grant request the end user just authorized, the honest end user
is redirected to the honest client instance. The honest client
instance can then detect that the end user is not the party that
started the request, since the request at the honest client instance
was started by the attacker. This detection can prevent the attack.
This is related to the discussion in Section 13.15, because again the
attack can be prevented by the AS informing the user as much as
possible about the client instance that is to be authorized.
If the end user does not interact with the client instance through a
web browser or the interaction start method does not use the same
browser or device that the end user is interacting through (such as
the launch of a second device through a scannable code or
presentation of a user code) the client instance will not be able to
strongly associate an incoming HTTP request with an established
session with the end user. This is also true when the push
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interaction finish method is used, since the HTTP request comes
directly from the interaction component of the AS. In these
circumstances, the client instance can at least ensure that the
incoming HTTP request can be uniquely associated with an ongoing
grant request by making the interaction finish callback URI unique
for the grant when making the interaction request (Section 2.5.2).
Mobile applications and other client instances that generally serve
only a single end user at a time can use this unique incoming URL to
differentiate between a legitimate incoming request and an attacker's
stolen request.
13.25. Calculating Interaction Hash
While the use of GNAP's signing mechanisms and token-protected grant
API provides significant security protections to the protocol, the
interaction reference mechanism is susceptible to monitoring,
capture, and injection by an attacker. To combat this, GNAP requires
the calculation and verification of an interaction hash. A client
instance might be tempted to skip this step, but doing so leaves the
client instance open to injection and manipulation by an attacker
that could lead to additional issues.
The calculation of the interaction hash value provides defense in
depth, allowing a client instance to protect itself from spurious
injection of interaction references when using an interaction finish
method. The AS is protected during this attack through the
continuation access token being bound to the expected interaction
reference, but without hash calculation, the attacker could cause the
client to make an HTTP request on command, which could itself be
manipulated -- for example, by including a malicious value in the
interaction reference designed to attack the AS. With both of these
in place, an attacker attempting to substitute the interaction
reference is stopped in several places.
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.----. .------. +--------+ +--------+
| User | |Attacker| | Client | | AS |
| | | | |Instance| | |
| | | | | | | |
| | | +=(1)=>| | | |
| | | | | +-(2)->| |
| | | | | |<-(3)-+ |
| | | |<=(4)=+ | | |
| | | | | | | |
| | | +==(5)================>| |
| | | | | | | |
| | | |<================(6)==+ |
| | | | | | | |
| +==(A)================>| | | |
| | | | | +-(B)->| |
| | | | | |<-(C)-+ |
| |<=================(D)=+ | | |
| | | | | | | |
| +==(E)================================>| |
| | | | | | | |
| |<=(7)=+ | | | | |
| | | | | | | |
| +==(F)================>| | | |
| | | | | +-(G)->| |
| | | | | | | |
`----` `------` +--------+ +--------+
Figure 11: Figure 11: Interaction hash attack
* Prerequisites: The client instance can allow multiple end users to
access the same AS. The attacker is attempting to associate their
rights with the target user's session.
* (1) The attacker starts a session at the client instance.
* (2) The client instance creates a grant request with nonce CN1.
* (3) The AS responds to the grant request with a need to interact,
nonce SN1, and a continuation token, CT1.
* (4) The client instructs the attacker to interact at the AS.
* (5) The attacker interacts at the AS.
* (6) The AS completes the interact finish with interact ref IR1 and
interact hash IH1 calculated from (CN1 + SN1 + IR1 + AS). The
attacker prevents IR1 from returning to the client instance.
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* (A) The target user starts a session at the client instance.
* (B) The client instance creates a grant request with nonce CN2.
* (C) The AS responds to the grant request with a need to interact,
nonce SN2, and a continuation token, CT2.
* (D) The client instance instructs the user to interact at the AS.
* (E) The target user interacts at the AS.
* (7) Before the target user can complete their interaction, the
attacker delivers their own interact ref IR1 into the user's
session. The attacker cannot calculate the appropriate hash
because the attacker does not have access to CN2 and SN2.
* (F) The target user triggers the interaction finish in their own
session with the attacker's IR1.
* (G) If the client instance is checking the interaction hash, the
attack stops here because the hash calculation of (CN2 + SN2 + IR1
+ AS) will fail. If the client instance does not check the
interaction hash, the client instance will be tricked into
submitting the interaction reference to the AS. Here, the AS will
reject the interaction request because it is presented against CT2
and not CT1 as expected. However, an attacker who has potentially
injected CT1 as the value of CT2 would be able to continue the
attack.
Even with additional checks in place, client instances using
interaction finish mechanisms are responsible for checking the
interaction hash to provide security to the overall system.
13.26. Storage of Information During Interaction and Continuation
When starting an interactive grant request, a client application has
a number of protocol elements that it needs to manage, including
nonces, references, keys, access tokens, and other elements. During
the interaction process, the client instance usually hands control of
the user experience over to another component, be it the system
browser, another application, or some action the resource owner is
instructed to take on another device. In order for the client
instance to make its continuation call, it will need to recall all of
these protocol elements at a future time. Usually this means the
client instance will need to store these protocol elements in some
retrievable fashion.
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If the security protocol elements are stored on the end user's
device, such as in browser storage or in local application data
stores, capture and exfiltration of this information could allow an
attacker to continue a pending transaction instead of the client
instance. Client software can make use of secure storage mechanisms,
including hardware-based key and data storage, to prevent such
exfiltration.
Note that in GNAP, the client instance has to choose its interaction
finish URI prior to making the first call to the AS. As such, the
interaction finish URI will often have a unique identifier for the
ongoing request, allowing the client instance to access the correct
portion of its storage. Since this URI is passed to other parties
and often used through a browser, this URI should not contain any
security-sensitive information that would be valuable to an attacker,
such as any token identifier, nonce, or user information. Instead, a
cryptographically random value is suggested, and that value should be
used to index into a secure session or storage mechanism.
13.27. Denial of Service (DoS) through Grant Continuation
When a client instance starts off an interactive process, it will
eventually need to continue the grant request in a subsequent message
to the AS. It's possible for a naive client implementation to
continuously send continuation requests to the AS while waiting for
approval, especially if no interaction finish method is used. Such
constant requests could overwhelm the AS's ability to respond to both
these and other requests.
To mitigate this for well-behaved client software, the continuation
response contains a wait parameter that is intended to tell the
client instance how long it should wait until making its next
request. This value can be used to back off client software that is
checking too quickly by returning increasing wait times for a single
client instance.
If client software ignores the wait value and makes its continuation
calls too quickly, or if the client software assumes the absence of
the wait values means it should poll immediately, the AS can choose
to return errors to the offending client instance, including possibly
canceling the ongoing grant request. With well-meaning client
software these errors can indicate a need to change the client
software's programmed behavior.
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13.28. Exhaustion of Random Value Space
Several parts of the GNAP process make use of unguessable randomized
values, such as nonces, tokens, user codes, and randomized URIs.
Since these values are intended to be unique, a sufficiently powerful
attacker could make a large number of requests to trigger generation
of randomized values in an attempt to exhaust the random number
generation space. While this attack is particularly applicable to
the AS, client software could likewise be targeted by an attacker
triggering new grant requests against an AS.
To mitigate this, software can ensure that its random values are
chosen from a significantly large pool that exhaustion of that pool
is prohibitive for an attacker. Additionally, the random values can
be time-boxed in such a way as their validity windows are reasonably
short. Since many of the random values used within GNAP are used
within limited portions of the protocol, it is reasonable for a
particular random value to be valid for only a small amount of time.
For example, the nonces used for interaction finish hash calculation
need only to be valid while the client instance is waiting for the
finish callback and can be functionally expired when the interaction
has completed. Similarly, artifacts like access tokens and the
interaction reference can be limited to have lifetimes tied to their
functional utility. Finally, each different category of artifact
(nonce, token, reference, identifier, etc.) can be generated from a
separate random pool of values instead of a single global value
space.
13.29. Front-channel URIs
Some interaction methods in GNAP make use of URIs accessed through
the end user's browser, known collectively as front-channel
communication. These URIs are most notably present in the redirect
interaction start method and the redirect interaction finish mode.
Since these URIs are intended to be given to the end user, the end
user and their browser will be subjected to anything hosted at that
URI including viruses, malware, and phishing scams. This kind of
risk is inherent to all redirection-based protocols, including GNAP
when used in this way.
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When talking to a new or unknown AS, a client instance might want to
check the URI from the interaction start against a blocklist and warn
the end user before redirecting them. Many client instances will
provide an interstitial message prior to redirection in order to
prepare the user for control of the user experience being handed to
the domain of the AS, and such a method could be used to warn the
user of potential threats. For instance, a rogue AS impersonating a
well-known service provider. Client software can also prevent this
by managing an allowlist of known and trusted AS's.
Alternatively, an attacker could start a GNAP request with a known
and trusted AS but include their own attack site URI as the callback
for the redirect finish method. The attacker would then send the
interaction start URI to the victim and get them to click on it.
Since the URI is at the known AS, the victim is inclined to do so.
The victim will then be prompted to approve the attacker's
application, and in most circumstances the victim will then be
redirected to the attacker's site whether or not the user approved
the request. The AS could mitigate this partially by using a
blocklist and allowlist of interaction finish URIs during the client
instance's initial request, but this approach can be especially
difficult if the URI has any dynamic portion chosen by the client
software. The AS can couple these checks with policies associated
with the client instance that has been authenticated in the request.
If the AS has any doubt about the interaction finish URI, the AS can
provide an interstitial warning to the end user before processing the
redirect.
Ultimately, all protocols that use redirect-based communication
through the user's browser are susceptible to having an attacker try
to co-opt one or more of those URIs in order to harm the user. It is
the responsibility of the AS and the client software to provide
appropriate warnings, education, and mitigation to protect end users.
13.30. Processing Assertions
Identity assertions can be used in GNAP to convey subject
information, both from the AS to the client instance in a response
(Section 3.4) and from the client instance to the AS in a request
(Section 2.2). In both of these circumstances, when an assertion is
passed in GNAP, the receiver of the assertion needs to parse and
process the assertion. As assertions are complex artifacts with
their own syntax and security, special care needs to be taken to
prevent the assertion values from being used as an attack vector.
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All assertion processing needs to account for the security aspects of
the assertion format in use. In particular, the processor needs to
parse the assertion from a JSON string object, and apply the
appropriate cryptographic processes to ensure the integrity of the
assertion.
For example, when SAML 2 assertions are used, the receiver has to
parse an XML document. There are many well-known security
vulnerabilities in XML parsers, and the XML standard itself can be
attacked through the use of processing instructions and entity
expansions to cause problems with the processor. Therefore, any
system capable of processing SAML 2 assertions also needs to have a
secure and correct XML parser. In addition to this, the SAML 2
specification uses XML Signatures, which have their own
implementation problems that need to be accounted for. Similar
requirements exist for OpenID Connect's ID token, which is based on
the JSON Web Token (JWT) format and the related JSON Object Signing
And Encryption (JOSE) cryptography suite.
13.31. Stolen Token Replay
If a client instance can request tokens at multiple AS's, and the
client instance uses the same keys to make its requests across those
different AS's, then it is possible for an attacker to replay a
stolen token issued by an honest AS from a compromised AS, thereby
binding the stolen token to the client instance's key in a different
context. The attacker can manipulate the client instance into using
the stolen token at an RS, particularly at an RS that is expecting a
token from the honest AS. Since the honest AS issued the token and
the client instance presents the token with its expected bound key,
the attack succeeds.
This attack has several preconditions. In this attack, the attacker
does not need access to the client instance's key and cannot use the
stolen token directly at the RS, but the attacker is able to get the
access token value in some fashion. The client instance also needs
to be configured to talk to multiple AS's, including the attacker's
controlled AS. Finally, the client instance needs to be able to be
manipulated by the attacker to call the RS while using a token issued
from the stolen AS. The RS does not need to be compromised or made
to trust the attacker's AS.
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To protect against this attack, the client instance can use a
different key for each AS that it talks to. Since the replayed token
will be bound to the key used at the honest AS, the uncompromised RS
will reject the call since the client instance will be using the key
used at the attacker's AS instead with the same token. When the MTLS
key proofing method is used, a client instance can use self-signed
certificates to use a different key for each AS that it talks to, as
discussed in Section 13.4.
Additionally, the client instance can keep a strong association
between the RS and a specific AS that it trusts to issue tokens for
that RS. This strong binding also helps against some forms of AS
mix-up attacks (Section 13.12). Managing this binding is outside the
scope of GNAP core, but it can be managed either as a configuration
element for the client instance or dynamically through discovering
the AS from the RS (Section 9.1).
The details of this attack are available in [HELMSCHMIDT2022] with
additional discussion and considerations.
13.32. Self-contained Stateless Access Tokens
The contents and format of the access token are at the discretion of
the AS, and are opaque to the client instance within GNAP. As
discussed in the companion document,
[I-D.ietf-gnap-resource-servers], the AS and RS can make use of
stateless access tokens with an internal structure and format. These
access tokens allow an RS to validate the token without having to
make any external calls at runtime, allowing for benefits in some
deployments, the discussion of which are outside the scope of this
specification.
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However, the use of such self-contained access tokens has an effect
on the ability of the AS to provide certain functionality defined
within this specification. Specifically, since the access token is
self-contained, it is difficult or impossible for an AS to signal to
all RS's within an ecosystem when a specific access token has been
revoked. Therefore, an AS in such an ecosystem should probably not
offer token revocation functionality to client instances, since the
client instance's calls to such an endpoint is effectively
meaningless. However, a client instance calling the token revocation
function will also throw out its copy of the token, so such a placebo
endpoint might not be completely meaningless. Token rotation
similarly difficult because the AS has to revoke the old access token
after a rotation call has been made. If the access tokens are
completely self-contained and non-revocable, this means that there
will be a period of time during which both the old and new access
tokens are valid and usable, which is an increased security risk for
the environment.
These problems can be mitigated by keeping the validity time windows
of self-contained access tokens reasonably short, limiting the time
after a revocation event that a revoked token could be used.
Additionally, the AS could proactively signal to RS's under its
control identifiers for revoked tokens that have yet to expire. This
type of information push would be expected to be relatively small and
infrequent, and its implementation is outside the scope of this
specification.
13.33. Network Problems and Token and Grant Management
If a client instance makes a call to rotate an access token but the
network connection is dropped before the client instance receives the
response with the new access token, the system as a whole can end up
in an inconsistent state, where the AS has already rotated the old
access token and invalidated it, but the client instance only has
access to the invalidated access token and not the newly rotated
token value. If the client instance retries the rotation request, it
would fail because the client is no longer presenting a valid and
current access token. A similar situation can occur during grant
continuation, where the same client instance calls to continue or
update a grant request without successfully receiving the results of
the update.
To combat this, both grant Management (Section 5) and token
management (Section 6) can be designed to be idempotent, where
subsequent calls to the same function with the same credentials are
meant to produce the same results. For example, multiple calls to
rotate the same access token need to result in the same rotated token
value, within a reasonable time window.
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In practice, an AS can hold on to an old token value for such limited
purposes. For example, to support rotating access tokens over
unreliable networks, the AS receives the initial request to rotate an
access token and creates a new token value and returns it. The AS
also marks the old token value as having been used to create the
newly-rotated token value. If the AS sees the old token value within
a small enough time window, such as a few seconds since the first
rotation attempt, the AS can return the same rotated access token
value. Furthermore, once the system has seen the newly-rotated token
in use, the original token can be discarded because the client
instance has proved that it did receive the token. The result of
this is a system that is eventually self-consistent without placing
an undue complexity burden on the client instance to manage
problematic networks.
13.34. Server-side Request Forgery (SSRF)
There are several places within GNAP where a URI can be given to a
party causing it to fetch that URI during normal operation of the
protocol. If an attacker is able to control the value of one of
these URIs within the protocol, the attacker could cause the target
system to execute a request on a URI that is within reach of the
target system but normally unavailable to the attacker. For example,
an attacker sending a URL of http://localhost/admin to cause the
server to access an internal function on itself, or
https://192.168.0.14/ to call a service behind a firewall. Even if
the attacker does not gain access to the results of the call, the
side effects of such requests coming from a trusted host can be
problematic to the security and sanctity of such otherwise unexposed
endpoints. This can be particularly problematic if such a URI is
used to call non-HTTP endpoints, such as remote code execution
services local to the AS.
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In GNAP, the most vulnerable place in the core protocol is the
push-based post-interaction finish method (Section 4.2.2), as the
client instance is less trusted than the AS and can use this method
to make the AS call an arbitrary URI. While it is not required by
the protocol, the AS can fetch other client-instance provided URIs
such as the logo image or home page, for verification or privacy-
preserving purposes before displaying them to the resource owner as
part of a consent screen. Even if the AS does not fetch these URIs,
their use in GNAP's normal operation could cause an attack against
the end user's browser as it fetches these same attack URIs.
Furthermore, extensions to GNAP that allow or require URI fetch could
also be similarly susceptible, such as a system for having the AS
fetch a client instance's keys from a presented URI instead of the
client instance presenting the key by value. Such extensions are
outside the scope of this specification, but any system deploying
such an extension would need to be aware of this issue.
To help mitigate this problem, similar approaches to protecting
parties against malicious redirects (Section 13.29) can be used. For
example, all URIs that can result in a direct request being made by a
party in the protocol can be filtered through an allowlist or
blocklist. For example, an AS that supports the push based
interaction finish can compare the callback URI in the interaction
request to a known URI for a pre-registered client instance, or it
can ensure that the URI is not on a blocklist of sensitive URLs such
as internal network addresses. However, note that because these
types of calls happen outside of the view of human interaction, it is
not usually feasible to provide notification and warning to someone
before the request needs to be executed, as is the case with
redirection URLs. As such, SSRF is somewhat more difficult to manage
at runtime, and systems should generally refuse to fetch a URI if
unsure.
13.35. Multiple Key Formats
All keys presented by value are allowed to be in only a single
format. While it would seem beneficial to allow keys to be sent in
multiple formats, in case the receiver doesn't understand one or more
of the formats used, there would be security issues with such a
feature. If multiple keys formats were allowed, receivers of these
key definitions would need to be able to make sure that it's the same
key represented in each field and not simply use one of the key
formats without checking for equivalence. If equivalence were not
carefully checked, it is possible for an attacker to insert their own
key into one of the formats without needing to have control over the
other formats. This could potentially lead to a situation where one
key is used by part of the system (such as identifying the client
instance) and a different key in a different format in the same
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message is used for other things (such as calculating signature
validity). However, in such cases, it is impossible for the receiver
to ensure that all formats contain the same key information since it
is assumed that the receiver cannot understand all of the formats.
To combat this, all keys presented by value have to be in exactly one
supported format known by the receiver as discussed in Section 7.1.
In most cases, a client instance is going to be configured with its
keys in a single format, and it will simply present that format as-is
to the AS in its request. A client instance capable of multiple
formats can use AS discovery (Section 9) to determine which formats
are supported, if desired. An AS should be generous in supporting
many different key formats to allow different types of client
software and client instance deployments. An AS implementation
should try to support multiple formats to allow a variety of client
software to connect.
13.36. Asynchronous Interactions
GNAP allows the RO to be contacted by the AS asynchronously, outside
the regular flow of the protocol. This allows for some advanced use
cases, such as cross-user authentication or information release, but
such advanced use cases have some distinct issues that implementors
need to be fully aware of before using these features.
First, in many applications, the return of a subject information to
the client instance could indicate to the client instance that the
end-user is the party represented by that information, functionally
allowing the end-user to authenticate to the client application.
While the details of a fully functional authentication protocol are
outside the scope of GNAP, it is a common exercise for a client
instance to be requesting information about the end user. This is
facilitated by the several interaction methods (Section 4.1) defined
in GNAP that allow the end user to begin interaction directly with
the AS. However, when the subject of the information is
intentionally not the end-user, the client application will need some
way to differentiate between requests for authentication of the end
user and requests for information about a different user. Confusing
these states could lead to an attacker having their account
associated with a privileged user. Client instances can mitigate
this by having distinct code paths for primary end user
authentication and requesting subject information about secondary
users, such as in a call center. In such use cases, the client
software used by the resource owner (the caller) and the end-user
(the agent) are generally distinct, allowing the AS to differentiate
between the agent's corporate device making the request and the
caller's personal device approving the request.
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Second, RO's interacting asynchronously do not usually have the same
context as an end user in an application attempting to perform the
task needing authorization. As such, the asynchronous requests for
authorization coming to the RO from the AS might have very little to
do with what the RO is doing at the time. This situation can
consequently lead to authorization fatigue on the part of the RO,
where any incoming authorization request is quickly approved and
dispatched without the RO making a proper verification of the
request. An attacker can exploit this fatigue and get the RO to
authorize the attacker's system for access. To mitigate this, AS
systems deploying asynchronous authorization should only prompt the
RO when the RO is expecting such a request, and significant user
experience engineering efforts need to be employed to ensure the RO
can clearly make the appropriate security decision. Furthermore,
audit capability, and the ability to undo access decisions that may
be ongoing, is particularly important in the asynchronous case.
13.37. Compromised RS
An attacker may aim to gain access to confidential or sensitive
resources. The measures for hardening and monitoring resource server
systems (beyond protection with access tokens) is out of the scope of
this document, but the use of GNAP to protect a system does not
absolve the resource server of following best practices. GNAP
generally considers a breach can occur, and therefore advises to
prefer key-bound tokens whenever possible, which at least limits the
impact of access token leakage by a compromised or malicious RS.
13.38. AS-Provided Token Keys
While the most common token issuance pattern is to bind the access
token to the client instance's presented key, it is possible for the
AS to provide a binding key along with an access token, as shown by
the key field of the token response in Section 3.2.1. This practice
allows for an AS to generate and manage the keys associated with
tokens independently of the keys known to client instances.
If the key material is returned by value from the AS, then the client
instance will simply use this key value when presenting the token.
This can be exploited by an attacker to issue a compromised token to
an unsuspecting client, assuming that the client instance trusts the
attacker's AS to issue tokens for the target RS. In this attack, the
attacker first gets a token bound to a key under the attacker's
control. This token is likely bound to an authorization or account
controlled by the attacker. The attacker then re-issues that same
token to the client instance, this time acting as an AS. The
attacker can return their own key to the client instance, tricking
the client instance into using the attacker's token. Such an attack
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is also possible when the key is returned by reference, if the
attacker is able to provide a reference meaningful to the client
instance that references a key under the attacker's control. This
substitution attack is similar to some of the main issues found with
bearer tokens as discussed in Section 13.9.
Returning a key with an access token should be limited to only
circumstances where both the client and AS can be verified to be
honest, and further only when the tradeoff of not using a client
instance's own keys is worth the additional risk.
14. Privacy Considerations
The privacy considerations in this section are modeled after the list
of privacy threats in [RFC6973], "Privacy Considerations for Internet
Protocols", and either explain how these threats are mitigated or
advise how the threats relate to GNAP.
14.1. Surveillance
Surveillance is the observation or monitoring of an individual's
communications or activities. Surveillance can be conducted by
observers or eavesdroppers at any point along the communications
path.
GNAP assumes the TLS protection used throughout the spec is intact.
Without the protection of TLS, there are many points throughout the
use of GNAP that would lead to possible surveillance. Even with the
proper use of TLS, surveillance could occur by several parties
outside of the TLS-protected channels, as discussed in the sections
below.
14.1.1. Surveillance by the Client
The purpose of GNAP is to authorize clients to be able to access
information on behalf of a user. So while it is expected that the
client may be aware of the user's identity as well as data being
fetched for that user, in some cases the extent of the client may be
beyond what the user is aware of. For example, a client may be
implemented as multiple distinct pieces of software, such as a
logging service or a mobile app that reports usage data to an
external backend service. Each of these pieces could gain
information about the user without the user being aware of this
action.
When the client software uses a hosted asset for its components, such
as its logo image, the fetch of these assets can reveal user actions
to the host. If the AS presents the logo URI to the resource owner
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in a browser page, the browser will fetch the logo URL from the
authorization screen. This fetch will tell the host of the logo
image that someone is accessing an instance of the client software
and requesting access for it. This is particularly problematic when
the host of the asset is not the client software itself, such as when
a content delivery network is used.
14.1.2. Surveillance by the Authorization Server
The role of the authorization server is to manage the authorization
of client instances to protect access to the user's data. In this
role, the authorization server is by definition aware of each
authorization of a client instance by a user. When the authorization
server shares user information with the client instance, it needs to
make sure that it has the permission from that user to do so.
Additionally, as part of the authorization grant process, the
authorization server may be aware of which resource servers the
client intends to use an access token at. However, it is possible to
design a system using GNAP in which this knowledge is not made
available to the authorization server, such as by avoiding the use of
the locations object in the authorization request.
If the authorization server's implementation of access tokens is such
that it requires a resource server call back to the authorization
server to validate them, then the authorization server will be aware
of which resource servers are actively in use and by which users and
which clients. To avoid this possibility, the authorization server
would need to structure access tokens in such a way that they can be
validated by the resource server without notifying the authorization
server that the token is being validated.
14.2. Stored Data
Several parties in the GNAP process are expected to persist data at
least temporarily, if not semi-permanently, for the normal
functioning of the system. If compromised, this could lead to
exposure of sensitive information. This section documents the
potentially sensitive information each party in GNAP is expected to
store for normal operation. Naturally it is possible that any party
is storing information for longer than technically necessary of the
protocol mechanics (such as audit logs, etc).
The authorization server is expected to store subject identifiers for
users indefinitely, in order to be able to include them in the
responses to clients. The authorization server is also expected to
store client key identifiers associated with display information
about the client such as its name and logo.
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The client is expected to store its client instance key indefinitely,
in order to authenticate to the authorization server for the normal
functioning of the GNAP flows. Additionally, the client will be
temporarily storing artifacts issued by the authorization server
during a flow, and these artifacts ought to be discarded by the
client when the transaction is complete.
The resource server is not required to store any state for its normal
operation, as far as its part in implementing GNAP. Depending on the
implementation of access tokens, the resource server may need to
cache public keys from the authorization server in order to validate
access tokens.
14.3. Intrusion
Intrusion refers to the ability of various parties to send
unsolicited messages or cause denial of service for unrelated
parties.
If the resource owner is different from the end user, there is an
opportunity for the end user to cause unsolicited messages to be sent
to the resource owner if the system prompts the resource owner for
consent when an end user attempts to access their data.
The format and contents of subject identifiers are intentionally not
defined by GNAP. If the authorization server uses values for subject
identifiers that are also identifiers for communication channels,
(e.g. an email address or phone number), this opens up the
possibility for a client to learn this information when it was not
otherwise authorized to access this kind of data about the user.
14.4. Correlation
The threat of correlation is the combination of various pieces of
information related to an individual in a way that defies their
expectations of what others know about them.
14.4.1. Correlation by Clients
The biggest risk of correlation in GNAP is when an authorization
server returns stable consistent user identifiers to multiple
different applications. In this case, applications created by
different parties would be able to correlate these user identifiers
out of band in order to know which users they have in common.
The most common example of this in practice is tracking for
advertising purposes, such that a client shares their list of user
IDs with an ad platform that is then able to retarget ads to
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applications created by other parties. In contrast, a positive
example of correlation is a corporate acquisition where two
previously unrelated clients now do need to be able to identify the
same user between the two clients, such as when software systems are
intentionally connected by the end user.
Another means of correlation comes from the use of RS-first discovery
(Section 9.1). A client instance knowing nothing other than an RS's
URL could make an unauthenticated call to the RS and learn which AS
protects the resources there. If the client instance knows something
about the AS, such as it being a single-user AS or belonging to a
specific organization, the client instance could, through
association, learn things about the resource without ever gaining
access to the resource itself.
14.4.2. Correlation by Resource Servers
Unrelated resource servers also have an opportunity to correlate
users if the authorization server includes stable user identifiers in
access tokens or in access token introspection responses.
In some cases a resource server may not actually need to be able to
identify users, (such as a resource server providing access to a
company cafeteria menu which only needs to validate whether the user
is a current employee), so authorization servers should be thoughtful
of when user identifiers are actually necessary to communicate to
resource servers for the functioning of the system.
However, note that the lack of inclusion of a user identifier in an
access token may be a risk if there is a concern that two users may
voluntarily share access tokens between them in order to access
protected resources. For example, if a website wants to limit access
to only people over 18, and such does not need to know any user
identifiers, an access token may be issued by an AS contains only the
claim "over 18". If the user is aware that this access token doesn't
reference them individually, they may be willing to share the access
token with a user who is under 18 in order to let them get access to
the website. (Note that the binding of an access token to a non-
extractable client instance key also prevents the access token from
being voluntarily shared.)
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14.4.3. Correlation by Authorization Servers
Clients are expected to be identified by their client instance key.
If a particular client instance key is used at more than one
authorization server, this could open up the possibility for multiple
unrelated authorization servers to correlate client instances. This
is especially a problem in the common case where a client instance is
used by a single individual, as it would allow the authorization
servers to correlate that individual between them. If this is a
concern of a client, the client should use distinct keys with each
authorization server.
14.5. Disclosure in Shared References
Throughout many parts of GNAP, the parties pass shared references
between each other, sometimes in place of the values themselves. For
example the interact_ref value used throughout the flow. These
references are intended to be random strings and should not contain
any private or sensitive data that would potentially leak information
between parties.
15. References
15.1. Normative References
[BCP195] Moriarty, K. and S. Farrell, "Deprecating TLS 1.0 and TLS
1.1", BCP 195, RFC 8996, March 2021.
Sheffer, Y., Saint-Andre, P., and T. Fossati,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 9325, November 2022.
<https://www.rfc-editor.org/info/bcp195>
[HASH-ALG] IANA, "Named Information Hash Algorithm Registry", n.d.,
<https://www.iana.org/assignments/named-information/named-
information.xhtml#hash-alg>.
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
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[I-D.ietf-httpbis-digest-headers]
Polli, R. and L. Pardue, "Digest Fields", Work in
Progress, Internet-Draft, draft-ietf-httpbis-digest-
headers-13, 10 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
digest-headers-13>.
[I-D.ietf-httpbis-message-signatures]
Backman, A., Richer, J., and M. Sporny, "HTTP Message
Signatures", Work in Progress, Internet-Draft, draft-ietf-
httpbis-message-signatures-19, 26 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
message-signatures-19>.
[I-D.ietf-secevent-subject-identifiers]
Backman, A., Scurtescu, M., and P. Jain, "Subject
Identifiers for Security Event Tokens", Work in Progress,
Internet-Draft, draft-ietf-secevent-subject-identifiers-
18, 24 June 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-secevent-subject-identifiers-18>.
[OIDC] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0 incorporating
errata set 1", November 2014,
<https://openid.net/specs/openid-connect-core-1_0.html>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC2397] Masinter, L., "The "data" URL scheme", RFC 2397,
DOI 10.17487/RFC2397, August 1998,
<https://www.rfc-editor.org/rfc/rfc2397>.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<https://www.rfc-editor.org/rfc/rfc3339>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/rfc/rfc3986>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/rfc/rfc4648>.
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[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <https://www.rfc-editor.org/rfc/rfc5646>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/rfc/rfc6749>.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750,
DOI 10.17487/RFC6750, October 2012,
<https://www.rfc-editor.org/rfc/rfc6750>.
[RFC7468] Josefsson, S. and S. Leonard, "Textual Encodings of PKIX,
PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468,
April 2015, <https://www.rfc-editor.org/rfc/rfc7468>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/rfc/rfc7515>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/rfc/rfc7517>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/rfc/rfc8259>.
[RFC8705] Campbell, B., Bradley, J., Sakimura, N., and T.
Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication
and Certificate-Bound Access Tokens", RFC 8705,
DOI 10.17487/RFC8705, February 2020,
<https://www.rfc-editor.org/rfc/rfc8705>.
[RFC9111] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Caching", STD 98, RFC 9111,
DOI 10.17487/RFC9111, June 2022,
<https://www.rfc-editor.org/rfc/rfc9111>.
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[SAML2] Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocol for the OASIS Security Assertion
Markup Language (SAML) V2.0", March 2005,
<https://docs.oasis-open.org/security/saml/v2.0/saml-core-
2.0-os.pdf>.
15.2. Informative References
[AXELAND2021]
Axeland, Å. and O. Oueidat, "Security Analysis of Attack
Surfaces on the Grant Negotiation and Authorization
Protocol", 2021,
<https://odr.chalmers.se/handle/20.500.12380/304105>.
[HELMSCHMIDT2022]
Helmschmidt, F., "Security Analysis of the Grant
Negotiation and Authorization Protocol", 2022,
<http://dx.doi.org/10.18419/opus-12203>.
[I-D.ietf-gnap-resource-servers]
Richer, J. and F. Imbault, "Grant Negotiation and
Authorization Protocol Resource Server Connections", Work
in Progress, Internet-Draft, draft-ietf-gnap-resource-
servers-04, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-gnap-
resource-servers-04>.
[I-D.ietf-oauth-security-topics]
Lodderstedt, T., Bradley, J., Labunets, A., and D. Fett,
"OAuth 2.0 Security Best Current Practice", Work in
Progress, Internet-Draft, draft-ietf-oauth-security-
topics-25, 8 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-oauth-
security-topics-25>.
[I-D.ietf-uta-rfc6125bis]
Saint-Andre, P. and R. Salz, "Service Identity in TLS",
Work in Progress, Internet-Draft, draft-ietf-uta-
rfc6125bis-15, 10 August 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-uta-
rfc6125bis-15>.
[promise-theory]
Burgess, M. and J. Bergstra, "Promise theory", January
2014, <http://markburgess.org/promises.html>.
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[RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic
Key Management", BCP 107, RFC 4107, DOI 10.17487/RFC4107,
June 2005, <https://www.rfc-editor.org/rfc/rfc4107>.
[RFC6202] Loreto, S., Saint-Andre, P., Salsano, S., and G. Wilkins,
"Known Issues and Best Practices for the Use of Long
Polling and Streaming in Bidirectional HTTP", RFC 6202,
DOI 10.17487/RFC6202, April 2011,
<https://www.rfc-editor.org/rfc/rfc6202>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/rfc/rfc6973>.
[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
DOI 10.17487/RFC7518, May 2015,
<https://www.rfc-editor.org/rfc/rfc7518>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[RFC8707] Campbell, B., Bradley, J., and H. Tschofenig, "Resource
Indicators for OAuth 2.0", RFC 8707, DOI 10.17487/RFC8707,
February 2020, <https://www.rfc-editor.org/rfc/rfc8707>.
[RFC8792] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
<https://www.rfc-editor.org/rfc/rfc8792>.
[RFC9396] Lodderstedt, T., Richer, J., and B. Campbell, "OAuth 2.0
Rich Authorization Requests", RFC 9396,
DOI 10.17487/RFC9396, May 2023,
<https://www.rfc-editor.org/rfc/rfc9396>.
[RFC9440] Campbell, B. and M. Bishop, "Client-Cert HTTP Header
Field", RFC 9440, DOI 10.17487/RFC9440, July 2023,
<https://www.rfc-editor.org/rfc/rfc9440>.
[SP80063C] Grassi, P., Nadeau, E., Richer, J., Squire, S., Fenton,
J., Lefkovitz, N., Danker, J., Choong, Y., Greene, K., and
M. Theofanos, "Digital Identity Guidelines: Federation and
Assertions", June 2017,
<https://doi.org/10.6028/NIST.SP.800-63c>.
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Appendix A. Document History
Note: To be removed by RFC editor before publication.
* 18
- Updates from IESG reviews.
* 17
- Updates from IESG reviews.
* 16
- Updates from AD review.
- Added security considerations on token substitution attack.
* 15
- Editorial updates from shepherd review.
- Clarify character set constraints of user codes.
* 14
- Update token rotation to use URI + management token.
- Fix key rotation with HTTP Signatures based on security
analysis.
* -13
- Editoral changes from chair review.
- Clarify that user codes are ungessable.
- Fix user code examples.
- Clarify expectations for extensions to interaction start and
finish methods.
- Fix references.
- Add IANA designated expert instructions.
- Clarify new vs. updated access tokens, and call out no need for
refresh tokens in OAuth 2 comparison section.
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- Add instructions on assertion processing.
- Explicitly list user reference lifetime management.
* -12
- Make default hash algorithm SHA256 instead of SHA3-512.
- Remove previous_key from key rotation.
- Defined requirements for key rotation methods.
- Add specificity to context of subject identifier being the AS.
- Editorial updates and protocol clarification.
* -11
- Error as object or string, more complete set of error codes
- Added key rotation in token management.
- Restrict keys to a single format per message.
- Discussed security issues of multiple key formats.
- Make token character set more strict.
- Add note on long-polling in continuation requests.
- Removed "Models" section.
- Rewrote guidance and requirements for extensions.
- Require all URIs to be absolute throughout protocol.
- Make response from RS a "SHOULD" instead of a "MAY".
- Added a way for the client instance to ask for a specific
user's information, separate from the end-user.
- Added security considerations for asynchronous authorization.
- Added security considerations for compromised RS.
- Added interoperability profiles.
- Added implementation status section.
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* -10
- Added note on relating access rights sent as strings to rights
sent as objects.
- Expand proofing methods to allow definition by object, with
single string as optimization for common cases.
- Removed "split_token" functionality.
- Collapse "user_code" into a string instead of an object.
- References hash algorithm identifiers from the existing IANA
registry
- Allow interaction responses to time out.
- Added explicit protocol state discussion.
- Added RO policy use case.
* -09
- Added security considerations on redirection status codes.
- Added security considerations on cuckoo token attack.
- Made token management URL required on token rotation.
- Added considerations on token rotation and self-contained
tokens.
- Added security considerations for SSRF.
- Moved normative requirements about end user presence to
security considerations.
- Clarified default wait times for continuation requests
(including polling).
- Clarified URI vs. URL.
- Added "user_code_uri" mode, removed "uri" from "user_code"
mode.
- Consistently formatted all parameter lists.
- Updated examples for HTTP Signatures.
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* -08
- Update definition for "Client" to account for the case of no
end user.
- Change definition for "Subject".
- Expanded security and privacy considerations for more
situations.
- Added cross-links from security and privacy considerations.
- Editorial updates.
* -07
- Replace user handle by opaque identifier
- Added trust relationships
- Added privacy considerations section
- Added security considerations.
* -06
- Removed "capabilities" and "existing_grant" protocol fields.
- Removed separate "instance_id" field.
- Split "interaction_methods_supported" into
"interaction_start_modes_supported" and
"interaction_finish_methods_supported".
- Added AS endpoint to hash calculation to fix mix-up attack.
- Added "privileges" field to resource access request object.
- Moved client-facing RS response back from GNAP-RS document.
- Removed oauthpop key binding.
- Removed dpop key binding.
- Added example DID identifier.
- Changed token response booleans to flag structure to match
request.
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- Updated signature examples to use HTTP Message Signatures.
* -05
- Changed "interaction_methods" to
"interaction_methods_supported".
- Changed "key_proofs" to "key_proofs_supported".
- Changed "assertions" to "assertions_supported".
- Updated discovery and field names for subject formats.
- Add an appendix to provide protocol rationale, compared to
OAuth2.
- Updated subject information definition.
- Refactored the RS-centric components into a new document.
- Updated cryptographic proof of possession methods to match
current reference syntax.
- Updated proofing language to use "signer" and "verifier"
generically.
- Updated cryptographic proof of possession examples.
- Editorial cleanup and fixes.
- Diagram cleanup and fixes.
* -04
- Updated terminology.
- Refactored key presentation and binding.
- Refactored "interact" request to group start and end modes.
- Changed access token request and response syntax.
- Changed DPoP digest field to 'htd' to match proposed FAPI
profile.
- Include the access token hash in the DPoP message.
- Removed closed issue links.
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- Removed function to read state of grant request by client.
- Closed issues related to reading and updating access tokens.
* -03
- Changed "resource client" terminology to separate "client
instance" and "client software".
- Removed OpenID Connect "claims" parameter.
- Dropped "short URI" redirect.
- Access token is mandatory for continuation.
- Removed closed issue links.
- Editorial fixes.
* -02
- Moved all "editor's note" items to GitHub Issues.
- Added JSON types to fields.
- Changed "GNAP Protocol" to "GNAP".
- Editorial fixes.
* -01
- "updated_at" subject info timestamp now in ISO 8601 string
format.
- Editorial fixes.
- Added Aaron and Fabien as document authors.
* -00
- Initial working group draft.
Appendix B. Compared to OAuth 2.0
GNAP's protocol design differs from OAuth 2.0's in several
fundamental ways:
1. *Consent and authorization flexibility:*
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OAuth 2.0 generally assumes the user has access to a web browser.
The type of interaction available is fixed by the grant type, and
the most common interactive grant types start in the browser.
OAuth 2.0 assumes that the user using the client software is the
same user that will interact with the AS to approve access.
GNAP allows various patterns to manage authorizations and
consents required to fulfill this requested delegation, including
information sent by the client instance, information supplied by
external parties, and information gathered through the
interaction process. GNAP allows a client instance to list
different ways that it can start and finish an interaction, and
these can be mixed together as needed for different use cases.
GNAP interactions can use a browser, but don't have to. Methods
can use inter-application messaging protocols, out-of-band data
transfer, or anything else. GNAP allows extensions to define new
ways to start and finish an interaction, as new methods and
platforms are expected to become available over time. GNAP is
designed to allow the end user and the resource owner to be two
different people, but still works in the optimized case of them
being the same party.
2. *Intent registration and inline negotiation:*
OAuth 2.0 uses different "grant types" that start at different
endpoints for different purposes. Many of these require
discovery of several interrelated parameters.
GNAP requests all start with the same type of request to the same
endpoint at the AS. Next steps are negotiated between the client
instance and AS based on software capabilities, policies
surrounding requested access, and the overall context of the
ongoing request. GNAP defines a continuation API that allows the
client instance and AS to request and send additional information
from each other over multiple steps. This continuation API uses
the same access token protection that other GNAP-protected APIs
use. GNAP allows discovery to optimize the requests but it isn't
required thanks to the negotiation capabilities.
GNAP is able to handle the life-cycle of an authorization
request, and therefore simplifies the mental model surrounding
OAuth2. For instance, there's no need for refresh tokens when
the API enables proper rotation of access tokens.
3. *Client instances:*
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OAuth 2.0 requires all clients to be registered at the AS and to
use a client_id known to the AS as part of the protocol. This
client_id is generally assumed to be assigned by a trusted
authority during a registration process, and OAuth places a lot
of trust on the client_id as a result. Dynamic registration
allows different classes of clients to get a client_id at
runtime, even if they only ever use it for one request.
GNAP allows the client instance to present an unknown key to the
AS and use that key to protect the ongoing request. GNAP's
client instance identifier mechanism allows for pre-registered
clients and dynamically registered clients to exist as an
optimized case without requiring the identifier as part of the
protocol at all times.
4. *Expanded delegation:*
OAuth 2.0 defines the "scope" parameter for controlling access to
APIs. This parameter has been coopted to mean a number of
different things in different protocols, including flags for
turning special behavior on and off, including the return of data
apart from the access token. The "resource" indicator (defined
in [RFC8707]) and RAR extensions (as defined in [RFC9396]) expand
on the "scope" concept in similar but different ways.
GNAP defines a rich structure for requesting access (analogous to
RAR), with string references as an optimization (analogous to
scopes). GNAP defines methods for requesting directly-returned
user information, separate from API access. This information
includes identifiers for the current user and structured
assertions. The core GNAP protocol makes no assumptions or
demands on the format or contents of the access token, but the RS
extension allows a negotiation of token formats between the AS
and RS.
5. *Cryptography-based security:*
OAuth 2.0 uses shared bearer secrets, including the client_secret
and access token, and advanced authentication and sender
constraint have been built on after the fact in inconsistent
ways.
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In GNAP, all communication between the client instance and AS is
bound to a key held by the client instance. GNAP uses the same
cryptographic mechanisms for both authenticating the client (to
the AS) and binding the access token (to the RS and the AS).
GNAP allows extensions to define new cryptographic protection
mechanisms, as new methods are expected to become available over
time. GNAP does not have a notion of "public clients" because
key information can always be sent and used dynamically.
6. *Privacy and usable security:*
OAuth 2.0's deployment model assumes a strong binding between the
AS and the RS.
GNAP is designed to be interoperable with decentralized identity
standards and to provide a human-centric authorization layer. In
addition to the core protocol, GNAP supports various patterns of
communication between RSs and ASs through extensions. GNAP tries
to limit the odds of a consolidation to just a handful of super-
popular AS services.
Appendix C. Example Protocol Flows
The protocol defined in this specification provides a number of
features that can be combined to solve many different kinds of
authentication scenarios. This section seeks to show examples of how
the protocol would be applied for different situations.
Some longer fields, particularly cryptographic information, have been
truncated for display purposes in these examples.
C.1. Redirect-Based User Interaction
In this scenario, the user is the RO and has access to a web browser,
and the client instance can take front-channel callbacks on the same
device as the user. This combination is analogous to the OAuth 2.0
Authorization Code grant type.
The client instance initiates the request to the AS. Here the client
instance identifies itself using its public key.
POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
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{
"access_token": {
"access": [
{
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
}
],
},
"client": {
"key": {
"proof": "httpsig",
"jwk": {
"kty": "RSA",
"e": "AQAB",
"kid": "xyz-1",
"alg": "RS256",
"n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8..."
}
}
},
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return/123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
}
The AS processes the request and determines that the RO needs to
interact. The AS returns the following response giving the client
instance the information it needs to connect. The AS has also
indicated to the client instance that it can use the given instance
identifier to identify itself in future requests (Section 2.3.1).
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HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"interact": {
"redirect":
"https://server.example.com/interact/4CF492MLVMSW9MKM",
"finish": "MBDOFXG4Y5CVJCX821LH"
}
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue"
},
"instance_id": "7C7C4AZ9KHRS6X63AJAO"
}
The client instance saves the response and redirects the user to the
interaction start mode's "redirect" URI by sending the following HTTP
message to the user's browser.
HTTP 303 Found
Location: https://server.example.com/interact/4CF492MLVMSW9MKM
The user's browser fetches the AS's interaction URI. The user logs
in, is identified as the RO for the resource being requested, and
approves the request. Since the AS has a callback parameter that was
sent in the initial request's interaction finish method, the AS
generates the interaction reference, calculates the hash, and
redirects the user back to the client instance with these additional
values added as query parameters.
NOTE: '\' line wrapping per RFC 8792
HTTP 302 Found
Location: https://client.example.net/return/123455\
?hash=x-gguKWTj8rQf7d7i3w3UhzvuJ5bpOlKyAlVpLxBffY\
&interact_ref=4IFWWIKYBC2PQ6U56NL1
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The client instance receives this request from the user's browser.
The client instance ensures that this is the same user that was sent
out by validating session information and retrieves the stored
pending request. The client instance uses the values in this to
validate the hash parameter. The client instance then calls the
continuation URI using the associated continuation access token and
presents the interaction reference in the request content. The
client instance signs the request as above.
POST /continue HTTP/1.1
Host: server.example.com
Content-Type: application/json
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
{
"interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}
The AS retrieves the pending request by looking up the pending grant
request associated with the presented continuation access token.
Seeing that the grant is approved, the AS issues an access token and
returns this to the client instance.
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NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
"access": [{
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
}]
},
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue"
}
}
C.2. Secondary Device Interaction
In this scenario, the user does not have access to a web browser on
the device and must use a secondary device to interact with the AS.
The client instance can display a user code or a printable QR code.
The client instance is not able to accept callbacks from the AS and
needs to poll for updates while waiting for the user to authorize the
request.
The client instance initiates the request to the AS.
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POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
{
"access_token": {
"access": [
"dolphin-metadata", "some other thing"
],
},
"client": "7C7C4AZ9KHRS6X63AJAO",
"interact": {
"start": ["redirect", "user_code"]
}
}
The AS processes this and determines that the RO needs to interact.
The AS supports both redirect URIs and user codes for interaction, so
it includes both. Since there is no interaction finish mode, the AS
does not include a nonce, but does include a "wait" parameter on the
continuation section because it expects the client instance to poll
for results.
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"interact": {
"redirect": "https://srv.ex/MXKHQ",
"user_code": {
"code": "A1BC3DFF"
}
},
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue/VGJKPTKC50",
"wait": 60
}
}
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The client instance saves the response and displays the user code
visually on its screen along with the static device URI. The client
instance also displays the short interaction URI as a QR code to be
scanned.
If the user scans the code, they are taken to the interaction
endpoint and the AS looks up the current pending request based on the
incoming URI. If the user instead goes to the static page and enters
the code manually, the AS looks up the current pending request based
on the value of the user code. In both cases, the user logs in, is
identified as the RO for the resource being requested, and approves
the request. Once the request has been approved, the AS displays to
the user a message to return to their device.
Meanwhile, the client instance periodically polls the AS every 60
seconds at the continuation URI. The client instance signs the
request using the same key and method that it did in the first
request.
POST /continue/VGJKPTKC50 HTTP/1.1
Host: server.example.com
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
The AS retrieves the pending request based on the pending grant
request associated with the continuation access token and determines
that it has not yet been authorized. The AS indicates to the client
instance that no access token has yet been issued but it can continue
to call after another 60 second timeout.
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"continue": {
"access_token": {
"value": "G7YQT4KQQ5TZY9SLSS5E"
},
"uri": "https://server.example.com/continue/ATWHO4Q1WV",
"wait": 60
}
}
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Note that the continuation URI and access token have been rotated
since they were used by the client instance to make this call. The
client instance polls the continuation URI after a 60 second timeout
using this new information.
POST /continue/ATWHO4Q1WV HTTP/1.1
Host: server.example.com
Authorization: GNAP G7YQT4KQQ5TZY9SLSS5E
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
The AS retrieves the pending request based on the URI and access
token, determines that it has been approved, and issues an access
token for the client to use at the RS.
NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
"access": [
"dolphin-metadata", "some other thing"
]
}
}
C.3. No User Involvement
In this scenario, the client instance is requesting access on its own
behalf, with no user to interact with.
The client instance creates a request to the AS, identifying itself
with its public key and using MTLS to make the request.
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POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
{
"access_token": {
"access": [
"backend service", "nightly-routine-3"
],
},
"client": {
"key": {
"proof": "mtls",
"cert#S256": "bwcK0esc3ACC3DB2Y5_lESsXE8o9ltc05O89jdN-dg2"
}
}
}
The AS processes this and determines that the client instance can ask
for the requested resources and issues an access token.
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": "https://server.example.com/token",
"access": [
"backend service", "nightly-routine-3"
]
}
}
C.4. Asynchronous Authorization
In this scenario, the client instance is requesting on behalf of a
specific RO, but has no way to interact with the user. The AS can
asynchronously reach out to the RO for approval in this scenario.
The client instance starts the request at the AS by requesting a set
of resources. The client instance also identifies a particular user.
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POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
{
"access_token": {
"access": [
{
"type": "photo-api",
"actions": [
"read",
"write",
"dolphin"
],
"locations": [
"https://server.example.net/",
"https://resource.local/other"
],
"datatypes": [
"metadata",
"images"
]
},
"read", "dolphin-metadata",
{
"type": "financial-transaction",
"actions": [
"withdraw"
],
"identifier": "account-14-32-32-3",
"currency": "USD"
},
"some other thing"
],
},
"client": "7C7C4AZ9KHRS6X63AJAO",
"user": {
"sub_ids": [ {
"format": "opaque",
"id": "J2G8G8O4AZ"
} ]
}
}
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The AS processes this and determines that the RO needs to interact.
The AS determines that it can reach the identified user
asynchronously and that the identified user does have the ability to
approve this request. The AS indicates to the client instance that
it can poll for continuation.
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"continue": {
"access_token": {
"value": "80UPRY5NM33OMUKMKSKU"
},
"uri": "https://server.example.com/continue",
"wait": 60
}
}
The AS reaches out to the RO and prompts them for consent. In this
example, the AS has an application that it can push notifications in
to for the specified account.
Meanwhile, the client instance periodically polls the AS every 60
seconds at the continuation URI.
POST /continue HTTP/1.1
Host: server.example.com
Authorization: GNAP 80UPRY5NM33OMUKMKSKU
Signature-Input: sig1=...
Signature: sig1=...
The AS retrieves the pending request based on the continuation access
token and determines that it has not yet been authorized. The AS
indicates to the client instance that no access token has yet been
issued but it can continue to call after another 60 second timeout.
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HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"continue": {
"access_token": {
"value": "BI9QNW6V9W3XFJK4R02D"
},
"uri": "https://server.example.com/continue",
"wait": 60
}
}
Note that the continuation access token value has been rotated since
it was used by the client instance to make this call. The client
instance polls the continuation URI after a 60 second timeout using
the new token.
POST /continue HTTP/1.1
Host: server.example.com
Authorization: GNAP BI9QNW6V9W3XFJK4R02D
Signature-Input: sig1=...
Signature: sig1=...
The AS retrieves the pending request based on the handle and
determines that it has been approved and it issues an access token.
NOTE: '\' line wrapping per RFC 8792
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
{
"access_token": {
"value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
"manage": "https://server.example.com/token/PRY5NM33O\
M4TB8N6BW7OZB8CDFONP219RP1L",
"access": [
"dolphin-metadata", "some other thing"
]
}
}
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C.5. Applying OAuth 2.0 Scopes and Client IDs
While GNAP is not designed to be directly compatible with OAuth 2.0
[RFC6749], considerations have been made to enable the use of OAuth
2.0 concepts and constructs more smoothly within GNAP.
In this scenario, the client developer has a client_id and set of
scope values from their OAuth 2.0 system and wants to apply them to
the new protocol. Traditionally, the OAuth 2.0 client developer
would put their client_id and scope values as parameters into a
redirect request to the authorization endpoint.
NOTE: '\' line wrapping per RFC 8792
HTTP 302 Found
Location: https://server.example.com/authorize\
?client_id=7C7C4AZ9KHRS6X63AJAO\
&scope=read%20write%20dolphin\
&redirect_uri=https://client.example.net/return\
&response_type=code\
&state=123455
Now the developer wants to make an analogous request to the AS using
GNAP. To do so, the client instance makes an HTTP POST and places
the OAuth 2.0 values in the appropriate places.
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POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
Signature-Input: sig1=...
Signature: sig1=...
Content-Digest: sha-256=...
{
"access_token": {
"access": [
"read", "write", "dolphin"
],
"flags": [ "bearer" ]
},
"client": "7C7C4AZ9KHRS6X63AJAO",
"interact": {
"start": ["redirect"],
"finish": {
"method": "redirect",
"uri": "https://client.example.net/return?state=123455",
"nonce": "LKLTI25DK82FX4T4QFZC"
}
}
}
The client_id can be used to identify the client instance's keys that
it uses for authentication, the scopes represent resources that the
client instance is requesting, and the redirect_uri and state value
are pre-combined into a finish URI that can be unique per request.
The client instance additionally creates a nonce to protect the
callback, separate from the state parameter that it has added to its
return URI.
From here, the protocol continues as above.
Appendix D. Interoperability Profiles
The GNAP specification has many different modes, options, and
mechanisms, allowing it to solve a wide variety of problems in a wide
variety of deployments. The wide applicability of GNAP makes it
difficult, if not impossible, to define a set of mandatory-to-
implement features, since one environment's required feature would be
impossible to do in another environment. While this is a large
problem in many systems, GNAP's back-and-forth negotiation process
allows parties to declare at runtime everything that they support and
then have the other party select from that the subset of items that
they also support, leading to functional compatibility in many parts
of the protocol even in an open world scenario.
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In addition, GNAP defines a set of interoperability profiles which
gather together core requirements to fix options into common
configurations that are likely to be useful to large populations of
similar applications.
Conformant AS implementations of these profiles MUST implement at
least the features as specified in the profile and MAY implement
additional features or profiles. Conformant client implementations
of these profiles MUST implement at least the features as specified,
except where a subset of the features allows the protocol to function
(such as using polling instead of a push finish method for the
Secondary Device profile).
D.1. Web-based Redirection
Implementations conformant to the Web-based Redirection profile of
GNAP MUST implement all of the following features:
* _Interaction Start Methods_: redirect
* _Interaction Finish Methods_: redirect
* _Interaction Hash Algorithms_: sha-256
* _Key Proofing Methods_: httpsig with no additional parameters
* _Key Formats_: jwks with signature algorithm included in the key's
alg parameter
* _JOSE Signature Algorithm_: PS256
* _Subject Identifier Formats_: opaque
* _Assertion Formats_: id_token
D.2. Secondary Device
Implementations conformant to the Secondary Device profile of GNAP
MUST implement all of the following features:
* _Interaction Start Methods_: user_code and user_code_uri
* _Interaction Finish Methods_: push
* _Interaction Hash Algorithms_: sha-256
* _Key Proofing Methods_: httpsig with no additional parameters
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* _Key Formats_: jwks with signature algorithm included in the key's
alg parameter
* _JOSE Signature Algorithm_: PS256
* _Subject Identifier Formats_: opaque
* _Assertion Formats_: id_token
Appendix E. Guidance for Extensions
Extensions to this specification have a variety of places to alter
the protocol, including many fields and objects that can have
additional values in a registry registry (Section 11) established by
this specification. For interoperability and to preserve the
security of the protocol, extensions should register new values with
IANA by following the specified mechanism. While it may technically
be possible to extend the protocol by adding elements to JSON objects
that are not governed by an IANA registry, a recipient may ignore
such values but is also allowed to reject them.
Most object fields in GNAP are specified with types, and those types
can allow different but related behavior. For example, the access
array can include either strings or objects, as discussed in
Section 8. The use of JSON polymorphism (Appendix F) within GNAP
allows extensions to define new fields by not only choosing a new
name but also by using an existing name with a new type. However,
the extension's definition of a new type for a field needs to fit the
same kind of item being extended. For example, a hypothetical
extension could define a string value for the access_token request
field, with a URL to download a hosted access token request. Such an
extension would be appropriate as the access_token field still
defines the access tokens being requested. However, if an extension
were to define a string value for the access_token request field,
with the value instead being something unrelated to the access token
request such as a value or key format, this would not be an
appropriate means of extension. (Note that this specific extension
example would create another form of SSRF attack surface as discussed
in Section 13.34.)
For another example, both interaction interaction start modes
(Section 2.5.1) and key proofing methods (Section 7.3) can be defined
as either strings or objects. An extension could take a method
defined as a string, such as app, and define an object-based version
with additional parameters. This extension should still define a
method to launch an application on the end user's device, just like
app does when specified as a string.
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Additionally, the ability to deal with different types for a field is
not expected to be equal between an AS and client software, with the
client software being assumed to be both more varied and more
simplified than the AS. Furthermore, the nature of the negotiation
process in GNAP allows the AS more chance of recovery from unknown
situations and parameters. As such, any extensions that change the
type of any field returned to a client instance should only do so
when the client instance has indicated specific support for that
extension through some kind of request parameter.
Appendix F. JSON Structures and Polymorphism
GNAP makes use of polymorphism within the JSON [RFC8259] structures
used for the protocol. Each portion of this protocol is defined in
terms of the JSON data type that its values can take, whether it's a
string, object, array, boolean, or number. For some fields,
different data types offer different descriptive capabilities and are
used in different situations for the same field. Each data type
provides a different syntax to express the same underlying semantic
protocol element, which allows for optimization and simplification in
many common cases.
Even though JSON is often used to describe strongly typed structures,
JSON on its own is naturally polymorphic. In JSON, the named members
of an object have no type associated with them, and any data type can
be used as the value for any member. In practice, each member has a
semantic type that needs to make sense to the parties creating and
consuming the object. Within this protocol, each object member is
defined in terms of its semantic content, and this semantic content
might have expressions in different concrete data types for different
specific purposes. Since each object member has exactly one value in
JSON, each data type for an object member field is naturally mutually
exclusive with other data types within a single JSON object.
For example, a resource request for a single access token is composed
of an object of resource request descriptions while a request for
multiple access tokens is composed of an array whose member values
are all objects. Both of these represent requests for access, but
the difference in syntax allows the client instance and AS to
differentiate between the two request types in the same request.
Another form of polymorphism in JSON comes from the fact that the
values within JSON arrays need not all be of the same JSON data type.
However, within this protocol, each element within the array needs to
be of the same kind of semantic element for the collection to make
sense, even when the data types are different from each other.
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For example, each aspect of a resource request can be described using
an object with multiple dimensional components, or the aspect can be
requested using a string. In both cases, the resource request is
being described in a way that the AS needs to interpret, but with
different levels of specificity and complexity for the client
instance to deal with. An API designer can provide a set of common
access scopes as simple strings but still allow client software
developers to specify custom access when needed for more complex
APIs.
Extensions to this specification can use different data types for
defined fields, but each extension needs to not only declare what the
data type means, but also provide justification for the data type
representing the same basic kind of thing it extends. For example,
an extension declaring an "array" representation for a field would
need to explain how the array represents something akin to the non-
array element that it is replacing. See additional discussion in
Appendix E.
Authors' Addresses
Justin Richer (editor)
Bespoke Engineering
Email: ietf@justin.richer.org
URI: https://bspk.io/
Fabien Imbault
acert.io
Email: fabien.imbault@acert.io
URI: https://acert.io/
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