Internet DRAFT - draft-parecki-oauth-v2-1
draft-parecki-oauth-v2-1
OAuth Working Group D. Hardt
Internet-Draft SignIn.Org
Intended status: Standards Track A. Parecki
Expires: 6 January 2021 Okta
T. Lodderstedt
yes.com
5 July 2020
The OAuth 2.1 Authorization Framework
draft-parecki-oauth-v2-1-03
Abstract
The OAuth 2.1 authorization framework enables a third-party
application to obtain limited access to an HTTP service, either on
behalf of a resource owner by orchestrating an approval interaction
between the resource owner and the HTTP service, or by allowing the
third-party application to obtain access on its own behalf. This
specification replaces and obsoletes the OAuth 2.0 Authorization
Framework described in RFC 6749.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 6 January 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
Hardt, et al. Expires 6 January 2021 [Page 1]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2. Protocol Flow . . . . . . . . . . . . . . . . . . . . . . 7
1.3. Authorization Grant . . . . . . . . . . . . . . . . . . . 8
1.3.1. Authorization Code . . . . . . . . . . . . . . . . . 8
1.3.2. Client Credentials . . . . . . . . . . . . . . . . . 8
1.4. Access Token . . . . . . . . . . . . . . . . . . . . . . 9
1.5. Refresh Token . . . . . . . . . . . . . . . . . . . . . . 9
1.6. TLS Version . . . . . . . . . . . . . . . . . . . . . . . 11
1.7. HTTP Redirections . . . . . . . . . . . . . . . . . . . . 11
1.8. Interoperability . . . . . . . . . . . . . . . . . . . . 11
1.9. Notational Conventions . . . . . . . . . . . . . . . . . 12
2. Client Registration . . . . . . . . . . . . . . . . . . . . . 12
2.1. Client Types . . . . . . . . . . . . . . . . . . . . . . 13
2.2. Client Identifier . . . . . . . . . . . . . . . . . . . . 14
2.3. Client Authentication . . . . . . . . . . . . . . . . . . 15
2.3.1. Client Password . . . . . . . . . . . . . . . . . . . 15
2.3.2. Other Authentication Methods . . . . . . . . . . . . 16
2.4. Unregistered Clients . . . . . . . . . . . . . . . . . . 17
3. Protocol Endpoints . . . . . . . . . . . . . . . . . . . . . 17
3.1. Authorization Endpoint . . . . . . . . . . . . . . . . . 17
3.1.1. Response Type . . . . . . . . . . . . . . . . . . . . 18
3.1.2. Redirection Endpoint . . . . . . . . . . . . . . . . 18
3.2. Token Endpoint . . . . . . . . . . . . . . . . . . . . . 20
3.2.1. Client Authentication . . . . . . . . . . . . . . . . 21
3.3. Access Token Scope . . . . . . . . . . . . . . . . . . . 21
4. Obtaining Authorization . . . . . . . . . . . . . . . . . . . 22
4.1. Authorization Code Grant . . . . . . . . . . . . . . . . 22
4.1.1. Authorization Request . . . . . . . . . . . . . . . . 24
4.1.2. Authorization Response . . . . . . . . . . . . . . . 27
4.1.3. Access Token Request . . . . . . . . . . . . . . . . 30
4.1.4. Access Token Response . . . . . . . . . . . . . . . . 31
4.2. Client Credentials Grant . . . . . . . . . . . . . . . . 31
4.2.1. Authorization Request and Response . . . . . . . . . 32
4.2.2. Access Token Request . . . . . . . . . . . . . . . . 32
4.2.3. Access Token Response . . . . . . . . . . . . . . . . 33
4.3. Extension Grants . . . . . . . . . . . . . . . . . . . . 33
5. Issuing an Access Token . . . . . . . . . . . . . . . . . . . 34
5.1. Successful Response . . . . . . . . . . . . . . . . . . . 34
5.2. Error Response . . . . . . . . . . . . . . . . . . . . . 35
6. Refreshing an Access Token . . . . . . . . . . . . . . . . . 37
Hardt, et al. Expires 6 January 2021 [Page 2]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
6.1. Refresh Token Protection . . . . . . . . . . . . . . . . 38
7. Accessing Protected Resources . . . . . . . . . . . . . . . . 40
7.1. Access Token Types . . . . . . . . . . . . . . . . . . . 40
7.2. Bearer Tokens . . . . . . . . . . . . . . . . . . . . . . 41
7.2.1. Authenticated Requests . . . . . . . . . . . . . . . 41
7.2.2. The WWW-Authenticate Response Header Field . . . . . 43
7.2.3. Error Codes . . . . . . . . . . . . . . . . . . . . . 44
7.3. Error Response . . . . . . . . . . . . . . . . . . . . . 45
7.3.1. Extension Token Types . . . . . . . . . . . . . . . . 45
7.4. Access Token Security Considerations . . . . . . . . . . 45
7.4.1. Security Threats . . . . . . . . . . . . . . . . . . 46
7.4.2. Threat Mitigation . . . . . . . . . . . . . . . . . . 46
7.4.3. Summary of Recommendations . . . . . . . . . . . . . 48
7.4.4. Token Replay Prevention . . . . . . . . . . . . . . . 49
7.4.5. Access Token Privilege Restriction . . . . . . . . . 50
8. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 50
8.1. Defining Access Token Types . . . . . . . . . . . . . . . 50
8.2. Defining New Endpoint Parameters . . . . . . . . . . . . 51
8.3. Defining New Authorization Grant Types . . . . . . . . . 51
8.4. Defining New Authorization Endpoint Response Types . . . 51
8.5. Defining Additional Error Codes . . . . . . . . . . . . . 52
9. Security Considerations . . . . . . . . . . . . . . . . . . . 52
9.1. Client Authentication . . . . . . . . . . . . . . . . . . 53
9.1.1. Client Authentication of Native Apps . . . . . . . . 53
9.2. Registration of Native App Clients . . . . . . . . . . . 54
9.3. Client Impersonation . . . . . . . . . . . . . . . . . . 54
9.3.1. Impersonation of Native Apps . . . . . . . . . . . . 55
9.4. Access Tokens . . . . . . . . . . . . . . . . . . . . . . 55
9.4.1. Access Token Privilege Restriction . . . . . . . . . 56
9.4.2. Access Token Replay Prevention . . . . . . . . . . . 56
9.5. Refresh Tokens . . . . . . . . . . . . . . . . . . . . . 57
9.6. Client Impersonating Resource Owner . . . . . . . . . . . 57
9.7. Protecting Redirect-Based Flows . . . . . . . . . . . . . 58
9.7.1. Loopback Redirect Considerations in Native Apps . . . 58
9.7.2. HTTP 307 Redirect . . . . . . . . . . . . . . . . . . 59
9.8. Authorization Codes . . . . . . . . . . . . . . . . . . . 60
9.9. Request Confidentiality . . . . . . . . . . . . . . . . . 61
9.10. Ensuring Endpoint Authenticity . . . . . . . . . . . . . 61
9.11. Credentials-Guessing Attacks . . . . . . . . . . . . . . 62
9.12. Phishing Attacks . . . . . . . . . . . . . . . . . . . . 62
9.13. Fake External User-Agents in Native Apps . . . . . . . . 62
9.14. Malicious External User-Agents in Native Apps . . . . . . 63
9.15. Cross-Site Request Forgery . . . . . . . . . . . . . . . 63
9.16. Clickjacking . . . . . . . . . . . . . . . . . . . . . . 64
9.17. Code Injection and Input Validation . . . . . . . . . . . 65
9.18. Open Redirectors . . . . . . . . . . . . . . . . . . . . 65
9.18.1. Client as Open Redirector . . . . . . . . . . . . . 65
9.18.2. Authorization Server as Open Redirector . . . . . . 65
Hardt, et al. Expires 6 January 2021 [Page 3]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
9.19. Authorization Server Mix-Up Mitigation in Native Apps . . 66
9.20. Embedded User Agents in Native Apps . . . . . . . . . . . 66
9.21. Other Recommendations . . . . . . . . . . . . . . . . . . 67
10. Native Applications . . . . . . . . . . . . . . . . . . . . . 67
10.1. Using Inter-App URI Communication for OAuth in Native
Apps . . . . . . . . . . . . . . . . . . . . . . . . . . 68
10.2. Initiating the Authorization Request from a Native
App . . . . . . . . . . . . . . . . . . . . . . . . . . 69
10.3. Receiving the Authorization Response in a Native App . . 70
10.3.1. Private-Use URI Scheme Redirection . . . . . . . . . 70
10.3.2. Claimed "https" Scheme URI Redirection . . . . . . . 71
10.3.3. Loopback Interface Redirection . . . . . . . . . . . 71
11. Browser-Based Apps . . . . . . . . . . . . . . . . . . . . . 72
12. Differences from OAuth 2.0 . . . . . . . . . . . . . . . . . 72
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 73
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 73
14.1. Normative References . . . . . . . . . . . . . . . . . . 73
14.2. Informative References . . . . . . . . . . . . . . . . . 76
Appendix A. Augmented Backus-Naur Form (ABNF) Syntax . . . . . . 79
A.1. "client_id" Syntax . . . . . . . . . . . . . . . . . . . 79
A.2. "client_secret" Syntax . . . . . . . . . . . . . . . . . 79
A.3. "response_type" Syntax . . . . . . . . . . . . . . . . . 80
A.4. "scope" Syntax . . . . . . . . . . . . . . . . . . . . . 80
A.5. "state" Syntax . . . . . . . . . . . . . . . . . . . . . 80
A.6. "redirect_uri" Syntax . . . . . . . . . . . . . . . . . . 80
A.7. "error" Syntax . . . . . . . . . . . . . . . . . . . . . 80
A.8. "error_description" Syntax . . . . . . . . . . . . . . . 80
A.9. "error_uri" Syntax . . . . . . . . . . . . . . . . . . . 81
A.10. "grant_type" Syntax . . . . . . . . . . . . . . . . . . . 81
A.11. "code" Syntax . . . . . . . . . . . . . . . . . . . . . . 81
A.12. "access_token" Syntax . . . . . . . . . . . . . . . . . . 81
A.13. "token_type" Syntax . . . . . . . . . . . . . . . . . . . 81
A.14. "expires_in" Syntax . . . . . . . . . . . . . . . . . . . 81
A.15. "refresh_token" Syntax . . . . . . . . . . . . . . . . . 81
A.16. Endpoint Parameter Syntax . . . . . . . . . . . . . . . . 82
A.17. "code_verifier" Syntax . . . . . . . . . . . . . . . . . 82
A.18. "code_challenge" Syntax . . . . . . . . . . . . . . . . . 82
Appendix B. Use of application/x-www-form-urlencoded Media
Type . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Appendix C. Extensions . . . . . . . . . . . . . . . . . . . . . 83
Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 84
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 84
Hardt, et al. Expires 6 January 2021 [Page 4]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
1. Introduction
In the traditional client-server authentication model, the client
requests an access-restricted resource (protected resource) on the
server by authenticating with the server using the resource owner's
credentials. In order to provide third-party applications access to
restricted resources, the resource owner shares its credentials with
the third party. This creates several problems and limitations:
* Third-party applications are required to store the resource
owner's credentials for future use, typically a password in clear-
text.
* Servers are required to support password authentication, despite
the security weaknesses inherent in passwords.
* Third-party applications gain overly broad access to the resource
owner's protected resources, leaving resource owners without any
ability to restrict duration or access to a limited subset of
resources.
* Resource owners cannot revoke access to an individual third party
without revoking access to all third parties, and must do so by
changing the third party's password.
* Compromise of any third-party application results in compromise of
the end-user's password and all of the data protected by that
password.
OAuth addresses these issues by introducing an authorization layer
and separating the role of the client from that of the resource
owner. In OAuth, the client requests access to resources controlled
by the resource owner and hosted by the resource server, and is
issued a different set of credentials than those of the resource
owner.
Instead of using the resource owner's credentials to access protected
resources, the client obtains an access token - a string denoting a
specific scope, lifetime, and other access attributes. Access tokens
are issued to third-party clients by an authorization server with the
approval of the resource owner. The client uses the access token to
access the protected resources hosted by the resource server.
Hardt, et al. Expires 6 January 2021 [Page 5]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
For example, an end-user (resource owner) can grant a printing
service (client) access to her protected photos stored at a photo-
sharing service (resource server), without sharing her username and
password with the printing service. Instead, she authenticates
directly with a server trusted by the photo-sharing service
(authorization server), which issues the printing service delegation-
specific credentials (access token).
This specification is designed for use with HTTP ([RFC7230]). The
use of OAuth over any protocol other than HTTP is out of scope.
Since the publication of the OAuth 2.0 Authorization Framework
([RFC6749]) in October 2012, it has been updated by OAuth 2.0 for
Native Apps ([RFC8252]), OAuth Security Best Current Practice
([I-D.ietf-oauth-security-topics]), and OAuth 2.0 for Browser-Based
Apps ([I-D.ietf-oauth-browser-based-apps]). The OAuth 2.0
Authorization Framework: Bearer Token Usage ([RFC6750]) has also been
updated with ([I-D.ietf-oauth-security-topics]). This Standards
Track specification consolidates the information in all of these
documents and removes features that have been found to be insecure in
[I-D.ietf-oauth-security-topics].
1.1. Roles
OAuth defines four roles:
"resource owner": An entity capable of granting access to a
protected resource. When the resource owner is a person, it is
referred to as an end-user. This is sometimes abbreviated as
"RO".
"resource server": The server hosting the protected resources,
capable of accepting and responding to protected resource requests
using access tokens. This is sometimes abbreviated as "RS".
"client": An application making protected resource requests on
behalf of the resource owner and with its authorization. The term
"client" does not imply any particular implementation
characteristics (e.g., whether the application executes on a
server, a desktop, or other devices).
"authorization server": The server issuing access tokens to the
client after successfully authenticating the resource owner and
obtaining authorization. This is sometimes abbreviated as "AS".
The interaction between the authorization server and resource server
is beyond the scope of this specification, however several extension
have been defined to provide an option for interoperability between
Hardt, et al. Expires 6 January 2021 [Page 6]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
resource servers and authorization servers. The authorization server
may be the same server as the resource server or a separate entity.
A single authorization server may issue access tokens accepted by
multiple resource servers.
1.2. Protocol Flow
+--------+ +---------------+
| |--(1)- Authorization Request ->| Resource |
| | | Owner |
| |<-(2)-- Authorization Grant ---| |
| | +---------------+
| |
| | +---------------+
| |--(3)-- Authorization Grant -->| Authorization |
| Client | | Server |
| |<-(4)----- Access Token -------| |
| | +---------------+
| |
| | +---------------+
| |--(5)----- Access Token ------>| Resource |
| | | Server |
| |<-(6)--- Protected Resource ---| |
+--------+ +---------------+
Figure 1: Abstract Protocol Flow
The abstract OAuth 2.1 flow illustrated in Figure 1 describes the
interaction between the four roles and includes the following steps:
1. The client requests authorization from the resource owner. The
authorization request can be made directly to the resource owner
(as shown), or preferably indirectly via the authorization server
as an intermediary.
2. The client receives an authorization grant, which is a credential
representing the resource owner's authorization, expressed using
one of two grant types defined in this specification or using an
extension grant type. The authorization grant type depends on
the method used by the client to request authorization and the
types supported by the authorization server.
3. The client requests an access token by authenticating with the
authorization server and presenting the authorization grant.
4. The authorization server authenticates the client and validates
the authorization grant, and if valid, issues an access token.
Hardt, et al. Expires 6 January 2021 [Page 7]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
5. The client requests the protected resource from the resource
server and authenticates by presenting the access token.
6. The resource server validates the access token, and if valid,
serves the request.
The preferred method for the client to obtain an authorization grant
from the resource owner (depicted in steps (1) and (2)) is to use the
authorization server as an intermediary, which is illustrated in
Figure 3 in Section 4.1.
1.3. Authorization Grant
An authorization grant is a credential representing the resource
owner's authorization (to access its protected resources) used by the
client to obtain an access token. This specification defines two
grant types - authorization code and client credentials - as well as
an extensibility mechanism for defining additional types.
1.3.1. Authorization Code
The authorization code is obtained by using an authorization server
as an intermediary between the client and resource owner. Instead of
requesting authorization directly from the resource owner, the client
directs the resource owner to an authorization server (via its user-
agent as defined in [RFC7231]), which in turn directs the resource
owner back to the client with the authorization code.
Before directing the resource owner back to the client with the
authorization code, the authorization server authenticates the
resource owner and obtains authorization. Because the resource owner
only authenticates with the authorization server, the resource
owner's credentials are never shared with the client.
The authorization code provides a few important security benefits,
such as the ability to authenticate the client, as well as the
transmission of the access token directly to the client without
passing it through the resource owner's user-agent and potentially
exposing it to others, including the resource owner.
1.3.2. Client Credentials
The client credentials (or other forms of client authentication) can
be used as an authorization grant when the authorization scope is
limited to the protected resources under the control of the client,
or to protected resources previously arranged with the authorization
server. Client credentials are used as an authorization grant
typically when the client is acting on its own behalf (the client is
Hardt, et al. Expires 6 January 2021 [Page 8]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
also the resource owner) or is requesting access to protected
resources based on an authorization previously arranged with the
authorization server.
1.4. Access Token
Access tokens are credentials used to access protected resources. An
access token is a string representing an authorization issued to the
client. The string is opaque to the client, but depending on the
authorization server, may be parseable by the resource server.
Tokens represent specific scopes and durations of access, granted by
the resource owner, and enforced by the resource server and
authorization server.
The token may denote an identifier used to retrieve the authorization
information or may self-contain the authorization information in a
verifiable manner (i.e., a token string consisting of some data and a
signature). One example of a structured token format is
[I-D.ietf-oauth-access-token-jwt], a method of encoding access token
data as a JSON Web Token [RFC7519].
Additional authentication credentials, which are beyond the scope of
this specification, may be required in order for the client to use a
token. This is typically referred to as a sender-constrained access
token, such as Mutual TLS Access Tokens [RFC8705].
The access token provides an abstraction layer, replacing different
authorization constructs (e.g., username and password) with a single
token understood by the resource server. This abstraction enables
issuing access tokens more restrictive than the authorization grant
used to obtain them, as well as removing the resource server's need
to understand a wide range of authentication methods.
Access tokens can have different formats, structures, and methods of
utilization (e.g., cryptographic properties) based on the resource
server security requirements. Access token attributes and the
methods used to access protected resources may be extended beyond
what is described in this specification.
1.5. Refresh Token
Refresh tokens are credentials used to obtain access tokens. Refresh
tokens are issued to the client by the authorization server and are
used to obtain a new access token when the current access token
becomes invalid or expires, or to obtain additional access tokens
with identical or narrower scope (access tokens may have a shorter
lifetime and fewer permissions than authorized by the resource
Hardt, et al. Expires 6 January 2021 [Page 9]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
owner). Issuing a refresh token is optional at the discretion of the
authorization server. If the authorization server issues a refresh
token, it is included when issuing an access token (i.e., step (4) in
Figure 2).
A refresh token is a string representing the authorization granted to
the client by the resource owner. The string is usually opaque to
the client. The token denotes an identifier used to retrieve the
authorization information. Unlike access tokens, refresh tokens are
intended for use only with authorization servers and are never sent
to resource servers.
+--------+ +---------------+
| |--(1)------- Authorization Grant --------->| |
| | | |
| |<-(2)----------- Access Token -------------| |
| | & Refresh Token | |
| | | |
| | +----------+ | |
| |--(3)---- Access Token ---->| | | |
| | | | | |
| |<-(4)- Protected Resource --| Resource | | Authorization |
| Client | | Server | | Server |
| |--(5)---- Access Token ---->| | | |
| | | | | |
| |<-(6)- Invalid Token Error -| | | |
| | +----------+ | |
| | | |
| |--(7)----------- Refresh Token ----------->| |
| | | |
| |<-(8)----------- Access Token -------------| |
+--------+ & Optional Refresh Token +---------------+
Figure 2: Refreshing an Expired Access Token
The flow illustrated in Figure 2 includes the following steps:
1. The client requests an access token by authenticating with the
authorization server and presenting an authorization grant.
2. The authorization server authenticates the client and validates
the authorization grant, and if valid, issues an access token and
optionally a refresh token.
3. The client makes a protected resource request to the resource
server by presenting the access token.
Hardt, et al. Expires 6 January 2021 [Page 10]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
4. The resource server validates the access token, and if valid,
serves the request.
5. Steps (3) and (4) repeat until the access token expires. If the
client knows the access token expired, it skips to step (7);
otherwise, it makes another protected resource request.
6. Since the access token is invalid, the resource server returns an
invalid token error.
7. The client requests a new access token by presenting the refresh
token and providing client authentication if it has been issued
credentials. The client authentication requirements are based on
the client type and on the authorization server policies.
8. The authorization server authenticates the client and validates
the refresh token, and if valid, issues a new access token (and,
optionally, a new refresh token).
1.6. TLS Version
Whenever Transport Layer Security (TLS) is used by this
specification, the appropriate version (or versions) of TLS will vary
over time, based on the widespread deployment and known security
vulnerabilities. At the time of this writing, TLS version 1.3
[RFC8446] is the most recent version.
Implementations MAY also support additional transport-layer security
mechanisms that meet their security requirements.
1.7. HTTP Redirections
This specification makes extensive use of HTTP redirections, in which
the client or the authorization server directs the resource owner's
user-agent to another destination. While the examples in this
specification show the use of the HTTP 302 status code, any other
method available via the user-agent to accomplish this redirection,
with the exception of HTTP 307, is allowed and is considered to be an
implementation detail. See Section 9.7.2 for details.
1.8. Interoperability
OAuth 2.1 provides a rich authorization framework with well-defined
security properties.
Hardt, et al. Expires 6 January 2021 [Page 11]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
This specification leaves a few required components partially or
fully undefined (e.g., client registration, authorization server
capabilities, endpoint discovery). Some of these behaviors are
defined in optional extensions which implementations can choose to
use.
Please refer to Appendix C for a list of current known extensions at
the time of this publication.
1.9. Notational Conventions
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 specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234]. Additionally, the rule URI-reference is
included from "Uniform Resource Identifier (URI): Generic Syntax"
[RFC3986].
Certain security-related terms are to be understood in the sense
defined in [RFC4949]. These terms include, but are not limited to,
"attack", "authentication", "authorization", "certificate",
"confidentiality", "credential", "encryption", "identity", "sign",
"signature", "trust", "validate", and "verify".
Unless otherwise noted, all the protocol parameter names and values
are case sensitive.
2. Client Registration
Before initiating the protocol, the client registers with the
authorization server. The means through which the client registers
with the authorization server are beyond the scope of this
specification but typically involve end-user interaction with an HTML
registration form, or by using Dynamic Client Registration
([RFC7591]).
Client registration does not require a direct interaction between the
client and the authorization server. When supported by the
authorization server, registration can rely on other means for
establishing trust and obtaining the required client properties
(e.g., redirect URI, client type). For example, registration can be
accomplished using a self-issued or third-party-issued assertion, or
by the authorization server performing client discovery using a
trusted channel.
Hardt, et al. Expires 6 January 2021 [Page 12]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
When registering a client, the client developer SHALL:
* specify the client type as described in Section 2.1,
* provide its client redirect URIs as described in Section 3.1.2,
and
* include any other information required by the authorization server
(e.g., application name, website, description, logo image, the
acceptance of legal terms).
Dynamic Client Registration ([RFC7591]) defines a common general data
model for clients that may be used even with manual client
registration.
2.1. Client Types
Clients are identified at the authorization server by a "client_id".
It is, for example, used by the authorization server to determine the
set of redirect URIs this client can use.
Clients requiring a higher level of confidence in their identity by
the authorization server use credentials to authenticate with the
authorization server. Such credentials are either issued by the
authorization server or registered by the developer of the client
with the authorization server.
OAuth 2.1 defines three client types:
"confidential": Clients that have credentials and their identity has
been confirmed by the AS are designated as "confidential clients"
"credentialed": Clients that have credentials and their identity has
been not been confirmed by the AS are designated as "credentialed
clients"
"public": Clients without credentials are called "public clients"
Any clients with credentials MUST take precautions to prevent leakage
and abuse of their credentials.
Authorization servers SHOULD consider the level of confidence in a
client's identity when deciding whether they allow such a client
access to more critical functions, such as the Client Credentials
grant type.
A single "client_id" MUST NOT be treated as more than one type of
client.
Hardt, et al. Expires 6 January 2021 [Page 13]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
This specification has been designed around the following client
profiles:
"web application": A web application is a confidential client
running on a web server. Resource owners access the client via an
HTML user interface rendered in a user-agent on the device used by
the resource owner. The client credentials as well as any access
token issued to the client are stored on the web server and are
not exposed to or accessible by the resource owner.
"browser-based application": A browser-based application is a public
client in which the client code is downloaded from a web server
and executes within a user-agent (e.g., web browser) on the device
used by the resource owner. Protocol data and credentials are
easily accessible (and often visible) to the resource owner.
Since such applications reside within the user-agent, they can
make seamless use of the user-agent capabilities when requesting
authorization.
"native application": A native application is a public client
installed and executed on the device used by the resource owner.
Protocol data and credentials are accessible to the resource
owner. It is assumed that any client authentication credentials
included in the application can be extracted. On the other hand,
dynamically issued credentials such as access tokens or refresh
tokens can receive an acceptable level of protection. At a
minimum, these credentials are protected from hostile servers with
which the application may interact. On some platforms, these
credentials might be protected from other applications residing on
the same device.
2.2. Client Identifier
The authorization server issues the registered client a client
identifier - a unique string representing the registration
information provided by the client. The client identifier is not a
secret; it is exposed to the resource owner and MUST NOT be used
alone for client authentication. The client identifier is unique to
the authorization server.
The client identifier string size is left undefined by this
specification. The client should avoid making assumptions about the
identifier size. The authorization server SHOULD document the size
of any identifier it issues.
Authorization servers SHOULD NOT allow clients to choose or influence
their "client_id" value. See Section 9.6 for details.
Hardt, et al. Expires 6 January 2021 [Page 14]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
2.3. Client Authentication
If the client has credentials, (is a confidential or credentialed
client), the client and authorization server establish a client
authentication method suitable for the security requirements of the
authorization server. The authorization server MAY accept any form
of client authentication meeting its security requirements.
Confidential and credentialed clients are typically issued (or
establish) a set of client credentials used for authenticating with
the authorization server (e.g., password, public/private key pair).
Authorization servers SHOULD use client authentication if possible.
It is RECOMMENDED to use asymmetric (public-key based) methods for
client authentication such as mTLS [RFC8705] or "private_key_jwt"
[OpenID]. When asymmetric methods for client authentication are
used, authorization servers do not need to store sensitive symmetric
keys, making these methods more robust against a number of attacks.
The authorization server MAY establish a client authentication method
with public clients, which converts them to credentialed clients.
However, the authorization server MUST NOT rely on credentialed
client authentication for the purpose of identifying the client.
The client MUST NOT use more than one authentication method in each
request.
2.3.1. Client Password
Clients in possession of a client password, also known as a client
secret, MAY use the HTTP Basic authentication scheme as defined in
[RFC2617] to authenticate with the authorization server. The client
identifier is encoded using the "application/x-www-form-urlencoded"
encoding algorithm per Appendix B, and the encoded value is used as
the username; the client secret is encoded using the same algorithm
and used as the password. The authorization server MUST support the
HTTP Basic authentication scheme for authenticating clients that were
issued a client secret.
For example (with extra line breaks for display purposes only):
Authorization: Basic czZCaGRSa3F0Mzo3RmpmcDBaQnIxS3REUmJuZlZkbUl3
Alternatively, the authorization server MAY support including the
client credentials in the request-body using the following
parameters:
Hardt, et al. Expires 6 January 2021 [Page 15]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
"client_id": REQUIRED. The client identifier issued to the client
during the registration process described by Section 2.2.
"client_secret": REQUIRED. The client secret.
Including the client credentials in the request-body using the two
parameters is NOT RECOMMENDED and SHOULD be limited to clients unable
to directly utilize the HTTP Basic authentication scheme (or other
password-based HTTP authentication schemes). The parameters can only
be transmitted in the request-body and MUST NOT be included in the
request URI.
For example, a request to refresh an access token (Section 6) using
the body parameters (with extra line breaks for display purposes
only):
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
grant_type=refresh_token&refresh_token=tGzv3JOkF0XG5Qx2TlKWIA
&client_id=s6BhdRkqt3&client_secret=7Fjfp0ZBr1KtDRbnfVdmIw
The authorization server MUST require the use of TLS as described in
Section 1.6 when sending requests using password authentication.
Since this client authentication method involves a password, the
authorization server MUST protect any endpoint utilizing it against
brute force attacks.
2.3.2. Other Authentication Methods
The authorization server MAY support any suitable authentication
scheme matching its security requirements. When using other
authentication methods, the authorization server MUST define a
mapping between the client identifier (registration record) and
authentication scheme.
Some additional authentication methods are defined in the "OAuth
Token Endpoint Authentication Methods
(https://www.iana.org/assignments/oauth-parameters/oauth-
parameters.xhtml#token-endpoint-auth-method)" registry, and may be
useful as generic client authentication methods beyond the specific
use of protecting the token endpoint.
Hardt, et al. Expires 6 January 2021 [Page 16]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
2.4. Unregistered Clients
This specification does not exclude the use of unregistered clients.
However, the use of such clients is beyond the scope of this
specification and requires additional security analysis and review of
its interoperability impact.
3. Protocol Endpoints
The authorization process utilizes two authorization server endpoints
(HTTP resources):
* Authorization endpoint - used by the client to obtain
authorization from the resource owner via user-agent redirection.
* Token endpoint - used by the client to exchange an authorization
grant for an access token, typically with client authentication.
As well as one client endpoint:
* Redirection endpoint - used by the authorization server to return
responses containing authorization credentials to the client via
the resource owner user-agent.
Not every authorization grant type utilizes both endpoints.
Extension grant types MAY define additional endpoints as needed.
3.1. Authorization Endpoint
The authorization endpoint is used to interact with the resource
owner and obtain an authorization grant. The authorization server
MUST first verify the identity of the resource owner. The way in
which the authorization server authenticates the resource owner
(e.g., username and password login, session cookies) is beyond the
scope of this specification.
The means through which the client obtains the location of the
authorization endpoint are beyond the scope of this specification,
but the location is typically provided in the service documentation,
or in the authorization server's metadata document ([RFC8414]).
The endpoint URI MAY include an "application/x-www-form-urlencoded"
formatted (per Appendix B) query component ([RFC3986] Section 3.4),
which MUST be retained when adding additional query parameters. The
endpoint URI MUST NOT include a fragment component.
Hardt, et al. Expires 6 January 2021 [Page 17]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
Since requests to the authorization endpoint result in user
authentication and the transmission of clear-text credentials (in the
HTTP response), the authorization server MUST require the use of TLS
as described in Section 1.6 when sending requests to the
authorization endpoint.
The authorization server MUST support the use of the HTTP "GET"
method [RFC7231] for the authorization endpoint and MAY support the
use of the "POST" method as well.
Parameters sent without a value MUST be treated as if they were
omitted from the request. The authorization server MUST ignore
unrecognized request parameters. Request and response parameters
defined by this specification MUST NOT be included more than once.
3.1.1. Response Type
The authorization endpoint is used by the authorization code flow.
The client informs the authorization server of the desired response
type using the following parameter:
"response_type": REQUIRED. The value MUST be "code" for requesting
an authorization code as described by Section 4.1.1, or a
registered extension value as described by Section 8.4.
Extension response types MAY contain a space-delimited (%x20) list of
values, where the order of values does not matter (e.g., response
type "a b" is the same as "b a"). The meaning of such composite
response types is defined by their respective specifications.
If an authorization request is missing the "response_type" parameter,
or if the response type is not understood, the authorization server
MUST return an error response as described in Section 4.1.2.1.
3.1.2. Redirection Endpoint
After completing its interaction with the resource owner, the
authorization server directs the resource owner's user-agent back to
the client. The authorization server redirects the user-agent to the
client's redirection endpoint previously established with the
authorization server during the client registration process.
The authorization server MUST compare the two URIs using simple
string comparison as defined in [RFC3986], Section 6.2.1.
The redirect URI MUST be an absolute URI as defined by [RFC3986]
Section 4.3. The endpoint URI MAY include an "application/x-www-
form-urlencoded" formatted (per Appendix B) query component
Hardt, et al. Expires 6 January 2021 [Page 18]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
([RFC3986] Section 3.4), which MUST be retained when adding
additional query parameters. The endpoint URI MUST NOT include a
fragment component.
3.1.2.1. Endpoint Request Confidentiality
The redirection endpoint SHOULD require the use of TLS as described
in Section 1.6 when the requested response type is "code", or when
the redirection request will result in the transmission of sensitive
credentials over an open network. If TLS is not available, the
authorization server SHOULD warn the resource owner about the
insecure endpoint prior to redirection (e.g., display a message
during the authorization request).
Lack of transport-layer security can have a severe impact on the
security of the client and the protected resources it is authorized
to access. The use of transport-layer security is particularly
critical when the authorization process is used as a form of
delegated end-user authentication by the client (e.g., third-party
sign-in service).
3.1.2.2. Registration Requirements
The authorization server MUST require all clients to register one or
more complete redirect URIs prior to utilizing the authorization
endpoint. The client MAY use the "state" request parameter to
achieve per-request customization if needed.
The authorization server MAY allow the client to register multiple
redirect URIs.
Lack of requiring registration of redirect URIs enables an attacker
to use the authorization endpoint as an open redirector as described
in Section 9.18.
3.1.2.3. Dynamic Configuration
If multiple redirect URIs have been registered the client MUST
include a redirect URI with the authorization request using the
"redirect_uri" request parameter.
3.1.2.4. Invalid Endpoint
If an authorization request fails validation due to a missing,
invalid, or mismatching redirect URI, the authorization server SHOULD
inform the resource owner of the error and MUST NOT automatically
redirect the user-agent to the invalid redirect URI.
Hardt, et al. Expires 6 January 2021 [Page 19]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
3.1.2.5. Endpoint Content
The redirection request to the client's endpoint typically results in
an HTML document response, processed by the user-agent. If the HTML
response is served directly as the result of the redirection request,
any script included in the HTML document will execute with full
access to the redirect URI and the credentials (e.g. authorization
code) it contains.
The client SHOULD NOT include any third-party scripts (e.g., third-
party analytics, social plug-ins, ad networks) in the redirection
endpoint response. Instead, it SHOULD extract the credentials from
the URI and redirect the user-agent again to another endpoint without
exposing the credentials (in the URI or elsewhere). If third-party
scripts are included, the client MUST ensure that its own scripts
(used to extract and remove the credentials from the URI) will
execute first.
3.2. Token Endpoint
The token endpoint is used by the client to obtain an access token by
presenting its authorization grant or refresh token.
The means through which the client obtains the location of the token
endpoint are beyond the scope of this specification, but the location
is typically provided in the service documentation, or in the
authorization server's metadata document ([RFC8414]).
The endpoint URI MAY include an "application/x-www-form-urlencoded"
formatted (per Appendix B) query component ([RFC3986] Section 3.4),
which MUST be retained when adding additional query parameters. The
endpoint URI MUST NOT include a fragment component.
Since requests to the token endpoint result in the transmission of
clear-text credentials (in the HTTP request and response), the
authorization server MUST require the use of TLS as described in
Section 1.6 when sending requests to the token endpoint.
The client MUST use the HTTP "POST" method when making access token
requests.
Parameters sent without a value MUST be treated as if they were
omitted from the request. The authorization server MUST ignore
unrecognized request parameters. Request and response parameters
defined by this specification MUST NOT be included more than once.
Hardt, et al. Expires 6 January 2021 [Page 20]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
3.2.1. Client Authentication
Confidential or credentialed clients client MUST authenticate with
the authorization server as described in Section 2.3 when making
requests to the token endpoint. Client authentication is used for:
* Enforcing the binding of refresh tokens and authorization codes to
the client they were issued to. Client authentication is critical
when an authorization code is transmitted to the redirection
endpoint over an insecure channel.
* Recovering from a compromised client by disabling the client or
changing its credentials, thus preventing an attacker from abusing
stolen refresh tokens. Changing a single set of client
credentials is significantly faster than revoking an entire set of
refresh tokens.
* Implementing authentication management best practices, which
require periodic credential rotation. Rotation of an entire set
of refresh tokens can be challenging, while rotation of a single
set of client credentials is significantly easier.
3.3. Access Token Scope
The authorization and token endpoints allow the client to specify the
scope of the access request using the "scope" request parameter. In
turn, the authorization server uses the "scope" response parameter to
inform the client of the scope of the access token issued.
The value of the scope parameter is expressed as a list of space-
delimited, case-sensitive strings. The strings are defined by the
authorization server. If the value contains multiple space-delimited
strings, their order does not matter, and each string adds an
additional access range to the requested scope.
scope = scope-token *( SP scope-token )
scope-token = 1*( %x21 / %x23-5B / %x5D-7E )
The authorization server MAY fully or partially ignore the scope
requested by the client, based on the authorization server policy or
the resource owner's instructions. If the issued access token scope
is different from the one requested by the client, the authorization
server MUST include the "scope" response parameter to inform the
client of the actual scope granted.
Hardt, et al. Expires 6 January 2021 [Page 21]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
If the client omits the scope parameter when requesting
authorization, the authorization server MUST either process the
request using a pre-defined default value or fail the request
indicating an invalid scope. The authorization server SHOULD
document its scope requirements and default value (if defined).
4. Obtaining Authorization
To request an access token, the client obtains authorization from the
resource owner. The authorization is expressed in the form of an
authorization grant, which the client uses to request the access
token. OAuth defines two grant types: authorization code and client
credentials. It also provides an extension mechanism for defining
additional grant types.
4.1. Authorization Code Grant
The authorization code grant type is used to obtain both access
tokens and refresh tokens.
Since this is a redirect-based flow, the client must be capable of
interacting with the resource owner's user-agent (typically a web
browser) and capable of receiving incoming requests (via redirection)
from the authorization server.
Hardt, et al. Expires 6 January 2021 [Page 22]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
+----------+
| Resource |
| Owner |
| |
+----------+
^
|
(2)
+----|-----+ Client Identifier +---------------+
| -+----(1)-- & Redirect URI ---->| |
| User- | | Authorization |
| Agent -+----(2)-- User authenticates --->| Server |
| | | |
| -+----(3)-- Authorization Code ---<| |
+-|----|---+ +---------------+
| | ^ v
(1) (3) | |
| | | |
^ v | |
+---------+ | |
| |>---(4)-- Authorization Code ---------' |
| Client | & Redirect URI |
| | |
| |<---(5)----- Access Token -------------------'
+---------+ (w/ Optional Refresh Token)
Note: The lines illustrating steps (1), (2), and (3) are broken into
two parts as they pass through the user-agent.
Figure 3: Authorization Code Flow
The flow illustrated in Figure 3 includes the following steps:
(1) The client initiates the flow by directing the resource owner's
user-agent to the authorization endpoint. The client includes its
client identifier, code challenge (derived from a generated code
verifier), optional requested scope, optional local state, and a
redirect URI to which the authorization server will send the user-
agent back once access is granted (or denied).
(2) The authorization server authenticates the resource owner (via
the user-agent) and establishes whether the resource owner grants or
denies the client's access request.
Hardt, et al. Expires 6 January 2021 [Page 23]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
(3) Assuming the resource owner grants access, the authorization
server redirects the user-agent back to the client using the redirect
URI provided earlier (in the request or during client registration).
The redirect URI includes an authorization code and any local state
provided by the client earlier.
(4) The client requests an access token from the authorization
server's token endpoint by including the authorization code received
in the previous step, and including its code verifier. When making
the request, the client authenticates with the authorization server
if it can. The client includes the redirect URI used to obtain the
authorization code for verification.
(5) The authorization server authenticates the client when possible,
validates the authorization code, validates the code verifier, and
ensures that the redirect URI received matches the URI used to
redirect the client in step (3). If valid, the authorization server
responds back with an access token and, optionally, a refresh token.
4.1.1. Authorization Request
To begin the authorization request, the client builds the
authorization request URI by adding parameters to the authorization
server's authorization endpoint URI.
Clients use a unique secret per authorization request to protect
against code injection and CSRF attacks. The client first generates
this secret, which it can later use along with the authorization code
to prove that the application using the authorization code is the
same application that requested it. The properties "code_challenge"
and "code_verifier" are adopted from the OAuth 2.0 extension known as
"Proof-Key for Code Exchange", or PKCE ([RFC7636]) where this
technique was originally developed.
Clients MUST use "code_challenge" and "code_verifier" and
authorization servers MUST enforce their use except under the
conditions described in Section 9.8. In this case, using and
enforcing "code_challenge" and "code_verifier" as described in the
following is still RECOMMENDED.
4.1.1.1. Client Creates a Code Verifier
The client first creates a code verifier, "code_verifier", for each
Authorization Request, in the following manner:
Hardt, et al. Expires 6 January 2021 [Page 24]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
code_verifier = high-entropy cryptographic random STRING using the
unreserved characters `[A-Z] / [a-z] / [0-9] / "-" / "." / "_" / "~"`
from Section 2.3 of {{RFC3986}}, with a minimum length of 43 characters
and a maximum length of 128 characters.
ABNF for "code_verifier" is as follows.
code-verifier = 43*128unreserved
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
ALPHA = %x41-5A / %x61-7A
DIGIT = %x30-39
NOTE: The code verifier SHOULD have enough entropy to make it
impractical to guess the value. It is RECOMMENDED that the output of
a suitable random number generator be used to create a 32-octet
sequence. The octet sequence is then base64url-encoded to produce a
43-octet URL-safe string to use as the code verifier.
4.1.1.2. Client Creates the Code Challenge
The client then creates a code challenge derived from the code
verifier by using one of the following transformations on the code
verifier:
plain
code_challenge = code_verifier
S256
code_challenge = BASE64URL-ENCODE(SHA256(ASCII(code_verifier)))
If the client is capable of using "S256", it MUST use "S256", as
"S256" is Mandatory To Implement (MTI) on the server. Clients are
permitted to use "plain" only if they cannot support "S256" for some
technical reason and know via out-of-band configuration or via
Authorization Server Metadata ([RFC8414]) that the server supports
"plain".
The plain transformation is for compatibility with existing
deployments and for constrained environments that can't use the
"S256" transformation.
ABNF for "code_challenge" is as follows.
code-challenge = 43*128unreserved
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
ALPHA = %x41-5A / %x61-7A
DIGIT = %x30-39
Hardt, et al. Expires 6 January 2021 [Page 25]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
4.1.1.3. Client Initiates the Authorization Request
The client constructs the request URI by adding the following
parameters to the query component of the authorization endpoint URI
using the "application/x-www-form-urlencoded" format, per Appendix B:
"response_type": REQUIRED. Value MUST be set to "code".
"client_id": REQUIRED. The client identifier as described in
Section 2.2.
"code_challenge": REQUIRED or RECOMMENDED (see Section 9.8). Code
challenge.
"code_challenge_method": OPTIONAL, defaults to "plain" if not
present in the request. Code verifier transformation method is
"S256" or "plain".
"redirect_uri": OPTIONAL. As described in Section 3.1.2.
"scope": OPTIONAL. The scope of the access request as described by
Section 3.3.
"state": OPTIONAL. An opaque value used by the client to maintain
state between the request and callback. The authorization server
includes this value when redirecting the user-agent back to the
client.
The client directs the resource owner to the constructed URI using an
HTTP redirection response, or by other means available to it via the
user-agent.
For example, the client directs the user-agent to make the following
HTTP request using TLS (with extra line breaks for display purposes
only):
GET /authorize?response_type=code&client_id=s6BhdRkqt3&state=xyz
&redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
&code_challenge=6fdkQaPm51l13DSukcAH3Mdx7_ntecHYd1vi3n0hMZY
&code_challenge_method=S256 HTTP/1.1
Host: server.example.com
The authorization server validates the request to ensure that all
required parameters are present and valid. If the request is valid,
the authorization server authenticates the resource owner and obtains
an authorization decision (by asking the resource owner or by
establishing approval via other means).
Hardt, et al. Expires 6 January 2021 [Page 26]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
When a decision is established, the authorization server directs the
user-agent to the provided client redirect URI using an HTTP
redirection response, or by other means available to it via the user-
agent.
4.1.2. Authorization Response
If the resource owner grants the access request, the authorization
server issues an authorization code and delivers it to the client by
adding the following parameters to the query component of the
redirect URI using the "application/x-www-form-urlencoded" format,
per Appendix B:
"code": REQUIRED. The authorization code generated by the
authorization server. The authorization code MUST expire shortly
after it is issued to mitigate the risk of leaks. A maximum
authorization code lifetime of 10 minutes is RECOMMENDED. The
client MUST NOT use the authorization code more than once. If an
authorization code is used more than once, the authorization
server MUST deny the request and SHOULD revoke (when possible) all
tokens previously issued based on that authorization code. The
authorization code is bound to the client identifier and redirect
URI.
"state": REQUIRED if the "state" parameter was present in the client
authorization request. The exact value received from the client.
For example, the authorization server redirects the user-agent by
sending the following HTTP response:
HTTP/1.1 302 Found
Location: https://client.example.com/cb?code=SplxlOBeZQQYbYS6WxSbIA
&state=xyz
The client MUST ignore unrecognized response parameters. The
authorization code string size is left undefined by this
specification. The client should avoid making assumptions about code
value sizes. The authorization server SHOULD document the size of
any value it issues.
When the server issues the authorization code in the authorization
response, it MUST associate the "code_challenge" and
"code_challenge_method" values with the authorization code so it can
be verified later.
Hardt, et al. Expires 6 January 2021 [Page 27]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
The "code_challenge" and "code_challenge_method" values may be stored
in encrypted form in the "code" itself, but could alternatively be
stored on the server associated with the code. The server MUST NOT
include the "code_challenge" value in client requests in a form that
other entities can extract.
The exact method that the server uses to associate the
"code_challenge" with the issued "code" is out of scope for this
specification.
4.1.2.1. Error Response
If the request fails due to a missing, invalid, or mismatching
redirect URI, or if the client identifier is missing or invalid, the
authorization server SHOULD inform the resource owner of the error
and MUST NOT automatically redirect the user-agent to the invalid
redirect URI.
An AS MUST reject requests without a "code_challenge" from public
clients, and MUST reject such requests from other clients unless
there is reasonable assurance that the client mitigates authorization
code injection in other ways. See Section 9.8 for details.
If the server does not support the requested "code_challenge_method"
transformation, the authorization endpoint MUST return the
authorization error response with "error" value set to
"invalid_request". The "error_description" or the response of
"error_uri" SHOULD explain the nature of error, e.g., transform
algorithm not supported.
If the resource owner denies the access request or if the request
fails for reasons other than a missing or invalid redirect URI, the
authorization server informs the client by adding the following
parameters to the query component of the redirect URI using the
"application/x-www-form-urlencoded" format, per Appendix B:
"error": REQUIRED. A single ASCII [USASCII] error code from the
following:
"invalid_request": The request is missing a required parameter,
includes an invalid parameter value, includes a parameter more
than once, or is otherwise malformed.
"unauthorized_client": The client is not authorized to request an
authorization code using this method.
"access_denied": The resource owner or authorization server
denied the request.
Hardt, et al. Expires 6 January 2021 [Page 28]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
"unsupported_response_type": The authorization server does not
support obtaining an authorization code using this method.
"invalid_scope": The requested scope is invalid, unknown, or
malformed.
"server_error": The authorization server encountered an
unexpected condition that prevented it from fulfilling the
request. (This error code is needed because a 500 Internal
Server Error HTTP status code cannot be returned to the client
via an HTTP redirect.)
"temporarily_unavailable": The authorization server is currently
unable to handle the request due to a temporary overloading or
maintenance of the server. (This error code is needed because
a 503 Service Unavailable HTTP status code cannot be returned
to the client via an HTTP redirect.)
Values for the "error" parameter MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E.
"error_description": OPTIONAL. Human-readable ASCII [USASCII] text
providing additional information, used to assist the client
developer in understanding the error that occurred. Values for
the "error_description" parameter MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E.
"error_uri": OPTIONAL. A URI identifying a human-readable web page
with information about the error, used to provide the client
developer with additional information about the error. Values for
the "error_uri" parameter MUST conform to the URI-reference syntax
and thus MUST NOT include characters outside the set %x21 /
%x23-5B / %x5D-7E.
"state": REQUIRED if a "state" parameter was present in the client
authorization request. The exact value received from the client.
For example, the authorization server redirects the user-agent by
sending the following HTTP response:
HTTP/1.1 302 Found
Location: https://client.example.com/cb?error=access_denied&state=xyz
Hardt, et al. Expires 6 January 2021 [Page 29]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
4.1.3. Access Token Request
The client makes a request to the token endpoint by sending the
following parameters using the "application/x-www-form-urlencoded"
format per Appendix B with a character encoding of UTF-8 in the HTTP
request entity-body:
"grant_type": REQUIRED. Value MUST be set to "authorization_code".
"code": REQUIRED. The authorization code received from the
authorization server.
"redirect_uri": REQUIRED, if the "redirect_uri" parameter was
included in the authorization request as described in
Section 4.1.1, and their values MUST be identical.
"client_id": REQUIRED, if the client is not authenticating with the
authorization server as described in Section 3.2.1.
"code_verifier": REQUIRED, if the "code_challenge" parameter was
included in the authorization request. MUST NOT be used
otherwise. The original code verifier string.
Confidential or credentialed clients MUST authenticate with the
authorization server as described in Section 3.2.1.
For example, the client makes the following HTTP request using TLS
(with extra line breaks for display purposes only):
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=authorization_code&code=SplxlOBeZQQYbYS6WxSbIA
&redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb
&code_verifier=3641a2d12d66101249cdf7a79c000c1f8c05d2aafcf14bf146497bed
The authorization server MUST:
* require client authentication for confidential and credentialed
clients (or clients with other authentication requirements),
* authenticate the client if client authentication is included,
* ensure that the authorization code was issued to the authenticated
confidential or credentialed client, or if the client is public,
ensure that the code was issued to "client_id" in the request,
Hardt, et al. Expires 6 January 2021 [Page 30]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
* verify that the authorization code is valid,
* verify that the "code_verifier" parameter is present if and only
if a "code_challenge" parameter was present in the authorization
request,
* if a "code_verifier" is present, verify the "code_verifier" by
calculating the code challenge from the received "code_verifier"
and comparing it with the previously associated "code_challenge",
after first transforming it according to the
"code_challenge_method" method specified by the client, and
* ensure that the "redirect_uri" parameter is present if the
"redirect_uri" parameter was included in the initial authorization
request as described in Section 4.1.1.3, and if included ensure
that their values are identical.
4.1.4. Access Token Response
If the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
token as described in Section 5.1. If the request client
authentication failed or is invalid, the authorization server returns
an error response as described in Section 5.2.
An example successful response:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache
{
"access_token": "2YotnFZFEjr1zCsicMWpAA",
"token_type": "Bearer",
"expires_in": 3600,
"refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
"example_parameter": "example_value"
}
4.2. Client Credentials Grant
The client can request an access token using only its client
credentials (or other supported means of authentication) when the
client is requesting access to the protected resources under its
control, or those of another resource owner that have been previously
arranged with the authorization server (the method of which is beyond
the scope of this specification).
Hardt, et al. Expires 6 January 2021 [Page 31]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
The client credentials grant type MUST only be used by confidential
or credentialed clients.
+---------+ +---------------+
| | | |
| |>--(1)- Client Authentication --->| Authorization |
| Client | | Server |
| |<--(2)---- Access Token ---------<| |
| | | |
+---------+ +---------------+
Figure 4: Client Credentials Flow
The flow illustrated in Figure 4 includes the following steps:
(1) The client authenticates with the authorization server and
requests an access token from the token endpoint.
(2) The authorization server authenticates the client, and if valid,
issues an access token.
4.2.1. Authorization Request and Response
Since the client authentication is used as the authorization grant,
no additional authorization request is needed.
4.2.2. Access Token Request
The client makes a request to the token endpoint by adding the
following parameters using the "application/x-www-form-urlencoded"
format per Appendix B with a character encoding of UTF-8 in the HTTP
request entity-body:
"grant_type": REQUIRED. Value MUST be set to "client_credentials".
"scope": OPTIONAL. The scope of the access request as described by
Section 3.3.
The client MUST authenticate with the authorization server as
described in Section 3.2.1.
For example, the client makes the following HTTP request using
transport-layer security (with extra line breaks for display purposes
only):
Hardt, et al. Expires 6 January 2021 [Page 32]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=client_credentials
The authorization server MUST authenticate the client.
4.2.3. Access Token Response
If the access token request is valid and authorized, the
authorization server issues an access token as described in
Section 5.1. A refresh token SHOULD NOT be included. If the request
failed client authentication or is invalid, the authorization server
returns an error response as described in Section 5.2.
An example successful response:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache
{
"access_token": "2YotnFZFEjr1zCsicMWpAA",
"token_type": "Bearer",
"expires_in": 3600,
"example_parameter": "example_value"
}
4.3. Extension Grants
The client uses an extension grant type by specifying the grant type
using an absolute URI (defined by the authorization server) as the
value of the "grant_type" parameter of the token endpoint, and by
adding any additional parameters necessary.
For example, to request an access token using the Device
Authorization Grant as defined by [RFC8628] after the user has
authorized the client on a separate device, the client makes the
following HTTP request using TLS (with extra line breaks for display
purposes only):
Hardt, et al. Expires 6 January 2021 [Page 33]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Adevice_code
&device_code=GmRhmhcxhwEzkoEqiMEg_DnyEysNkuNhszIySk9eS
&client_id=C409020731
If the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
token as described in Section 5.1. If the request failed client
authentication or is invalid, the authorization server returns an
error response as described in Section 5.2.
5. Issuing an Access Token
If the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
token as described in Section 5.1. If the request failed client
authentication or is invalid, the authorization server returns an
error response as described in Section 5.2.
5.1. Successful Response
The authorization server issues an access token and optional refresh
token, and constructs the response by adding the following parameters
to the entity-body of the HTTP response with a 200 (OK) status code:
"access_token": REQUIRED. The access token issued by the
authorization server.
"token_type": REQUIRED. The type of the token issued as described
in Section 7.1. Value is case insensitive.
"expires_in": RECOMMENDED. The lifetime in seconds of the access
token. For example, the value "3600" denotes that the access
token will expire in one hour from the time the response was
generated. If omitted, the authorization server SHOULD provide
the expiration time via other means or document the default value.
"refresh_token": OPTIONAL. The refresh token, which can be used to
obtain new access tokens using the same authorization grant as
described in Section 6.
"scope": OPTIONAL, if identical to the scope requested by the
client; otherwise, REQUIRED. The scope of the access token as
described by Section 3.3.
Hardt, et al. Expires 6 January 2021 [Page 34]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
The parameters are included in the entity-body of the HTTP response
using the "application/json" media type as defined by [RFC7159]. The
parameters are serialized into a JavaScript Object Notation (JSON)
structure by adding each parameter at the highest structure level.
Parameter names and string values are included as JSON strings.
Numerical values are included as JSON numbers. The order of
parameters does not matter and can vary.
The authorization server MUST include the HTTP "Cache-Control"
response header field [RFC7234] with a value of "no-store" in any
response containing tokens, credentials, or other sensitive
information, as well as the "Pragma" response header field [RFC7234]
with a value of "no-cache".
For example:
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache
{
"access_token":"2YotnFZFEjr1zCsicMWpAA",
"token_type":"Bearer",
"expires_in":3600,
"refresh_token":"tGzv3JOkF0XG5Qx2TlKWIA",
"example_parameter":"example_value"
}
The client MUST ignore unrecognized value names in the response. The
sizes of tokens and other values received from the authorization
server are left undefined. The client should avoid making
assumptions about value sizes. The authorization server SHOULD
document the size of any value it issues.
5.2. Error Response
The authorization server responds with an HTTP 400 (Bad Request)
status code (unless specified otherwise) and includes the following
parameters with the response:
"error": REQUIRED. A single ASCII [USASCII] error code from the
following:
"invalid_request": The request is missing a required parameter,
Hardt, et al. Expires 6 January 2021 [Page 35]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
includes an unsupported parameter value (other than grant
type), repeats a parameter, includes multiple credentials,
utilizes more than one mechanism for authenticating the client,
contains a "code_verifier" although no "code_challenge" was
sent in the authorization request, or is otherwise malformed.
"invalid_client": Client authentication failed (e.g., unknown
client, no client authentication included, or unsupported
authentication method). The authorization server MAY return an
HTTP 401 (Unauthorized) status code to indicate which HTTP
authentication schemes are supported. If the client attempted
to authenticate via the "Authorization" request header field,
the authorization server MUST respond with an HTTP 401
(Unauthorized) status code and include the "WWW-Authenticate"
response header field matching the authentication scheme used
by the client.
"invalid_grant": The provided authorization grant (e.g.,
authorization code, resource owner credentials) or refresh
token is invalid, expired, revoked, does not match the redirect
URI used in the authorization request, or was issued to another
client.
"unauthorized_client": The authenticated client is not authorized
to use this authorization grant type.
"unsupported_grant_type": The authorization grant type is not
supported by the authorization server.
"invalid_scope": The requested scope is invalid, unknown,
malformed, or exceeds the scope granted by the resource owner.
Values for the "error" parameter MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E.
"error_description": OPTIONAL. Human-readable ASCII [USASCII] text
providing additional information, used to assist the client
developer in understanding the error that occurred. Values for
the "error_description" parameter MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E.
"error_uri": OPTIONAL. A URI identifying a human-readable web page
with information about the error, used to provide the client
developer with additional information about the error. Values for
the "error_uri" parameter MUST conform to the URI-reference syntax
and thus MUST NOT include characters outside the set %x21 /
%x23-5B / %x5D-7E.
Hardt, et al. Expires 6 January 2021 [Page 36]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
The parameters are included in the entity-body of the HTTP response
using the "application/json" media type as defined by [RFC7159]. The
parameters are serialized into a JSON structure by adding each
parameter at the highest structure level. Parameter names and string
values are included as JSON strings. Numerical values are included
as JSON numbers. The order of parameters does not matter and can
vary.
For example:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache
{
"error":"invalid_request"
}
6. Refreshing an Access Token
Authorization servers SHOULD determine, based on a risk assessment,
whether to issue refresh tokens to a certain client. If the
authorization server decides not to issue refresh tokens, the client
MAY refresh access tokens by utilizing other grant types, such as the
authorization code grant type. In such a case, the authorization
server may utilize cookies and persistent grants to optimize the user
experience.
If refresh tokens are issued, those refresh tokens MUST be bound to
the scope and resource servers as consented by the resource owner.
This is to prevent privilege escalation by the legitimate client and
reduce the impact of refresh token leakage.
If the authorization server issued a refresh token to the client, the
client makes a refresh request to the token endpoint by adding the
following parameters using the "application/x-www-form-urlencoded"
format per Appendix B with a character encoding of UTF-8 in the HTTP
request entity-body:
"grant_type": REQUIRED. Value MUST be set to "refresh_token".
"refresh_token": REQUIRED. The refresh token issued to the client.
"scope": OPTIONAL. The scope of the access request as described by
Hardt, et al. Expires 6 January 2021 [Page 37]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
Section 3.3. The requested scope MUST NOT include any scope not
originally granted by the resource owner, and if omitted is
treated as equal to the scope originally granted by the resource
owner.
Because refresh tokens are typically long-lasting credentials used to
request additional access tokens, the refresh token is bound to the
client to which it was issued. Confidential or credentialed clients
MUST authenticate with the authorization server as described in
Section 3.2.1.
For example, the client makes the following HTTP request using
transport-layer security (with extra line breaks for display purposes
only):
POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded
grant_type=refresh_token&refresh_token=tGzv3JOkF0XG5Qx2TlKWIA
The authorization server MUST:
* require client authentication for confidential or credentialed
clients
* authenticate the client if client authentication is included and
ensure that the refresh token was issued to the authenticated
client, and
* validate the refresh token.
6.1. Refresh Token Protection
Authorization servers SHOULD utilize one of these methods to detect
refresh token replay by malicious actors for public clients:
* _Sender-constrained refresh tokens:_ the authorization server
cryptographically binds the refresh token to a certain client
instance by utilizing [I-D.ietf-oauth-token-binding], [RFC8705],
[I-D.ietf-oauth-dpop], or another suitable method.
* _Refresh token rotation:_ the authorization server issues a new
refresh token with every access token refresh response. The
previous refresh token is invalidated but information about the
relationship is retained by the authorization server. If a
refresh token is compromised and subsequently used by both the
Hardt, et al. Expires 6 January 2021 [Page 38]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
attacker and the legitimate client, one of them will present an
invalidated refresh token, which will inform the authorization
server of the breach. The authorization server cannot determine
which party submitted the invalid refresh token, but it will
revoke the active refresh token. This stops the attack at the
cost of forcing the legitimate client to obtain a fresh
authorization grant.
Implementation note: the grant to which a refresh token belongs may
be encoded into the refresh token itself. This can enable an
authorization server to efficiently determine the grant to which a
refresh token belongs, and by extension, all refresh tokens that need
to be revoked. Authorization servers MUST ensure the integrity of
the refresh token value in this case, for example, using signatures.
If valid and authorized, the authorization server issues an access
token as described in Section 5.1. If the request failed
verification or is invalid, the authorization server returns an error
response as described in Section 5.2.
The authorization server MAY issue a new refresh token, in which case
the client MUST discard the old refresh token and replace it with the
new refresh token. The authorization server MAY revoke the old
refresh token after issuing a new refresh token to the client. If a
new refresh token is issued, the refresh token scope MUST be
identical to that of the refresh token included by the client in the
request.
Authorization servers MAY revoke refresh tokens automatically in case
of a security event, such as:
* password change
* logout at the authorization server
Refresh tokens SHOULD expire if the client has been inactive for some
time, i.e., the refresh token has not been used to obtain fresh
access tokens for some time. The expiration time is at the
discretion of the authorization server. It might be a global value
or determined based on the client policy or the grant associated with
the refresh token (and its sensitivity).
Hardt, et al. Expires 6 January 2021 [Page 39]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
7. Accessing Protected Resources
The client accesses protected resources by presenting the access
token to the resource server. The resource server MUST validate the
access token and ensure that it has not expired and that its scope
covers the requested resource. The methods used by the resource
server to validate the access token (as well as any error responses)
are beyond the scope of this specification, but generally involve an
interaction or coordination between the resource server and the
authorization server, such as using Token Introspection [RFC7662] or
a structured access token format such as a JWT
[I-D.ietf-oauth-access-token-jwt].
The method in which the client utilizes the access token to
authenticate with the resource server depends on the type of access
token issued by the authorization server. Typically, it involves
using the HTTP "Authorization" request header field [RFC2617] with an
authentication scheme defined by the specification of the access
token type used, such as "Bearer", defined below.
7.1. Access Token Types
The access token type provides the client with the information
required to successfully utilize the access token to make a protected
resource request (along with type-specific attributes). The client
MUST NOT use an access token if it does not understand the token
type.
For example, the "Bearer" token type defined in this specification is
utilized by simply including the access token string in the request:
GET /resource/1 HTTP/1.1
Host: example.com
Authorization: Bearer mF_9.B5f-4.1JqM
The above example is provided for illustration purposes only.
Each access token type definition specifies the additional attributes
(if any) sent to the client together with the "access_token" response
parameter. It also defines the HTTP authentication method used to
include the access token when making a protected resource request.
Hardt, et al. Expires 6 January 2021 [Page 40]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
7.2. Bearer Tokens
A Bearer Token is a security token with the property that any party
in possession of the token (a "bearer") can use the token in any way
that any other party in possession of it can. Using a bearer token
does not require a bearer to prove possession of cryptographic key
material (proof-of-possession).
Bearer tokens may be extended to include proof-of-possession
techniques by other specifications.
7.2.1. Authenticated Requests
This section defines two methods of sending Bearer tokens in resource
requests to resource servers. Clients MUST NOT use more than one
method to transmit the token in each request.
7.2.1.1. Authorization Request Header Field
When sending the access token in the "Authorization" request header
field defined by HTTP/1.1 [RFC2617], the client uses the "Bearer"
authentication scheme to transmit the access token.
For example:
GET /resource HTTP/1.1
Host: server.example.com
Authorization: Bearer mF_9.B5f-4.1JqM
The syntax of the "Authorization" header field for this scheme
follows the usage of the Basic scheme defined in Section 2 of
[RFC2617]. Note that, as with Basic, it does not conform to the
generic syntax defined in Section 1.2 of [RFC2617] but is compatible
with the general authentication framework in HTTP 1.1 Authentication
[RFC7235], although it does not follow the preferred practice
outlined therein in order to reflect existing deployments. The
syntax for Bearer credentials is as follows:
b64token = 1*( ALPHA / DIGIT /
"-" / "." / "_" / "~" / "+" / "/" ) *"="
credentials = "Bearer" 1*SP b64token
Clients SHOULD make authenticated requests with a bearer token using
the "Authorization" request header field with the "Bearer" HTTP
authorization scheme. Resource servers MUST support this method.
Hardt, et al. Expires 6 January 2021 [Page 41]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
7.2.1.2. Form-Encoded Body Parameter
When sending the access token in the HTTP request entity-body, the
client adds the access token to the request-body using the
"access_token" parameter. The client MUST NOT use this method unless
all of the following conditions are met:
* The HTTP request entity-header includes the "Content-Type" header
field set to "application/x-www-form-urlencoded".
* The entity-body follows the encoding requirements of the
"application/x-www-form-urlencoded" content-type as defined by
HTML 4.01 [W3C.REC-html401-19991224].
* The HTTP request entity-body is single-part.
* The content to be encoded in the entity-body MUST consist entirely
of ASCII [USASCII] characters.
* The HTTP request method is one for which the request-body has
defined semantics. In particular, this means that the "GET"
method MUST NOT be used.
The entity-body MAY include other request-specific parameters, in
which case the "access_token" parameter MUST be properly separated
from the request-specific parameters using "&" character(s) (ASCII
code 38).
For example, the client makes the following HTTP request using
transport-layer security:
POST /resource HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
access_token=mF_9.B5f-4.1JqM
The "application/x-www-form-urlencoded" method SHOULD NOT be used
except in application contexts where participating clients do not
have access to the "Authorization" request header field. Resource
servers MAY support this method.
Hardt, et al. Expires 6 January 2021 [Page 42]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
7.2.2. The WWW-Authenticate Response Header Field
If the protected resource request does not include authentication
credentials or does not contain an access token that enables access
to the protected resource, the resource server MUST include the HTTP
"WWW-Authenticate" response header field; it MAY include it in
response to other conditions as well. The "WWW-Authenticate" header
field uses the framework defined by HTTP/1.1 [RFC2617].
All challenges defined by this specification MUST use the auth-scheme
value "Bearer". This scheme MUST be followed by one or more auth-
param values. The auth-param attributes used or defined by this
specification are as follows. Other auth-param attributes MAY be
used as well.
A "realm" attribute MAY be included to indicate the scope of
protection in the manner described in HTTP/1.1 [RFC2617]. The
"realm" attribute MUST NOT appear more than once.
The "scope" attribute is defined in Section 3.3. The "scope"
attribute is a space-delimited list of case-sensitive scope values
indicating the required scope of the access token for accessing the
requested resource. "scope" values are implementation defined; there
is no centralized registry for them; allowed values are defined by
the authorization server. The order of "scope" values is not
significant. In some cases, the "scope" value will be used when
requesting a new access token with sufficient scope of access to
utilize the protected resource. Use of the "scope" attribute is
OPTIONAL. The "scope" attribute MUST NOT appear more than once. The
"scope" value is intended for programmatic use and is not meant to be
displayed to end-users.
Two example scope values follow; these are taken from the OpenID
Connect [OpenID.Messages] and the Open Authentication Technology
Committee (OATC) Online Multimedia Authorization Protocol [OMAP]
OAuth 2.0 use cases, respectively:
scope="openid profile email"
scope="urn:example:channel=HBO&urn:example:rating=G,PG-13"
If the protected resource request included an access token and failed
authentication, the resource server SHOULD include the "error"
attribute to provide the client with the reason why the access
request was declined. The parameter value is described in
Section 7.2.3. In addition, the resource server MAY include the
"error_description" attribute to provide developers a human-readable
explanation that is not meant to be displayed to end-users. It also
MAY include the "error_uri" attribute with an absolute URI
Hardt, et al. Expires 6 January 2021 [Page 43]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
identifying a human-readable web page explaining the error. The
"error", "error_description", and "error_uri" attributes MUST NOT
appear more than once.
Values for the "scope" attribute (specified in Appendix A.4) MUST NOT
include characters outside the set %x21 / %x23-5B / %x5D-7E for
representing scope values and %x20 for delimiters between scope
values. Values for the "error" and "error_description" attributes
(specified in Appendixes A.7 and A.8) MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E. Values for the
"error_uri" attribute (specified in Appendix A.9 of) MUST conform to
the URI-reference syntax and thus MUST NOT include characters outside
the set %x21 / %x23-5B / %x5D-7E.
For example, in response to a protected resource request without
authentication:
HTTP/1.1 401 Unauthorized
WWW-Authenticate: Bearer realm="example"
And in response to a protected resource request with an
authentication attempt using an expired access token:
HTTP/1.1 401 Unauthorized
WWW-Authenticate: Bearer realm="example",
error="invalid_token",
error_description="The access token expired"
7.2.3. Error Codes
When a request fails, the resource server responds using the
appropriate HTTP status code (typically, 400, 401, 403, or 405) and
includes one of the following error codes in the response:
"invalid_request": The request is missing a required parameter,
includes an unsupported parameter or parameter value, repeats the
same parameter, uses more than one method for including an access
token, or is otherwise malformed. The resource server SHOULD
respond with the HTTP 400 (Bad Request) status code.
"invalid_token": The access token provided is expired, revoked,
malformed, or invalid for other reasons. The resource SHOULD
respond with the HTTP 401 (Unauthorized) status code. The client
MAY request a new access token and retry the protected resource
request.
"insufficient_scope": The request requires higher privileges than
Hardt, et al. Expires 6 January 2021 [Page 44]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
provided by the access token. The resource server SHOULD respond
with the HTTP 403 (Forbidden) status code and MAY include the
"scope" attribute with the scope necessary to access the protected
resource.
If the request lacks any authentication information (e.g., the client
was unaware that authentication is necessary or attempted using an
unsupported authentication method), the resource server SHOULD NOT
include an error code or other error information.
For example:
HTTP/1.1 401 Unauthorized
WWW-Authenticate: Bearer realm="example"
7.3. Error Response
If a resource access request fails, the resource server SHOULD inform
the client of the error. The method by which the resource server
does this is determined by the particular token type, such as the
description of Bearer tokens in Section 7.2.3.
7.3.1. Extension Token Types
[RFC6750] establishes a common registry in Section 11.4
(https://tools.ietf.org/html/rfc6749#section-11.4) for error values
to be shared among OAuth token authentication schemes.
New authentication schemes designed primarily for OAuth token
authentication SHOULD define a mechanism for providing an error
status code to the client, in which the error values allowed are
registered in the error registry established by this specification.
Such schemes MAY limit the set of valid error codes to a subset of
the registered values. If the error code is returned using a named
parameter, the parameter name SHOULD be "error".
Other schemes capable of being used for OAuth token authentication,
but not primarily designed for that purpose, MAY bind their error
values to the registry in the same manner.
New authentication schemes MAY choose to also specify the use of the
"error_description" and "error_uri" parameters to return error
information in a manner parallel to their usage in this
specification.
7.4. Access Token Security Considerations
Hardt, et al. Expires 6 January 2021 [Page 45]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
7.4.1. Security Threats
The following list presents several common threats against protocols
utilizing some form of tokens. This list of threats is based on NIST
Special Publication 800-63 [NIST800-63].
7.4.1.1. Token manufacture/modification
An attacker may generate a bogus token or modify the token contents
(such as the authentication or attribute statements) of an existing
token, causing the resource server to grant inappropriate access to
the client. For example, an attacker may modify the token to extend
the validity period; a malicious client may modify the assertion to
gain access to information that they should not be able to view.
7.4.1.2. Token disclosure
Tokens may contain authentication and attribute statements that
include sensitive information.
7.4.1.3. Token redirect
An attacker uses a token generated for consumption by one resource
server to gain access to a different resource server that mistakenly
believes the token to be for it.
7.4.1.4. Token replay
An attacker attempts to use a token that has already been used with
that resource server in the past.
7.4.2. Threat Mitigation
A large range of threats can be mitigated by protecting the contents
of the token by using a digital signature. Alternatively, a bearer
token can contain a reference to authorization information, rather
than encoding the information directly. Such references MUST be
infeasible for an attacker to guess; using a reference may require an
extra interaction between a server and the token issuer to resolve
the reference to the authorization information. The mechanics of
such an interaction are not defined by this specification.
This document does not specify the encoding or the contents of the
token; hence, detailed recommendations about the means of
guaranteeing token integrity protection are outside the scope of this
document. The token integrity protection MUST be sufficient to
prevent the token from being modified.
Hardt, et al. Expires 6 January 2021 [Page 46]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
To deal with token redirect, it is important for the authorization
server to include the identity of the intended recipients (the
audience), typically a single resource server (or a list of resource
servers), in the token. Restricting the use of the token to a
specific scope is also RECOMMENDED.
The authorization server MUST implement TLS. Which version(s) ought
to be implemented will vary over time and will depend on the
widespread deployment and known security vulnerabilities at the time
of implementation.
To protect against token disclosure, confidentiality protection MUST
be applied using TLS with a ciphersuite that provides confidentiality
and integrity protection. This requires that the communication
interaction between the client and the authorization server, as well
as the interaction between the client and the resource server,
utilize confidentiality and integrity protection. Since TLS is
mandatory to implement and to use with this specification, it is the
preferred approach for preventing token disclosure via the
communication channel. For those cases where the client is prevented
from observing the contents of the token, token encryption MUST be
applied in addition to the usage of TLS protection. As a further
defense against token disclosure, the client MUST validate the TLS
certificate chain when making requests to protected resources,
including checking the Certificate Revocation List (CRL) [RFC5280].
Cookies are typically transmitted in the clear. Thus, any
information contained in them is at risk of disclosure. Therefore,
Bearer tokens MUST NOT be stored in cookies that can be sent in the
clear, as any information in them is at risk of disclosure. See
"HTTP State Management Mechanism" [RFC6265] for security
considerations about cookies.
In some deployments, including those utilizing load balancers, the
TLS connection to the resource server terminates prior to the actual
server that provides the resource. This could leave the token
unprotected between the front-end server where the TLS connection
terminates and the back-end server that provides the resource. In
such deployments, sufficient measures MUST be employed to ensure
confidentiality of the token between the front-end and back-end
servers; encryption of the token is one such possible measure.
To deal with token capture and replay, the following recommendations
are made: First, the lifetime of the token MUST be limited; one means
of achieving this is by putting a validity time field inside the
protected part of the token. Note that using short-lived (one hour
or less) tokens reduces the impact of them being leaked. Second,
confidentiality protection of the exchanges between the client and
Hardt, et al. Expires 6 January 2021 [Page 47]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
the authorization server and between the client and the resource
server MUST be applied. As a consequence, no eavesdropper along the
communication path is able to observe the token exchange.
Consequently, such an on-path adversary cannot replay the token.
Furthermore, when presenting the token to a resource server, the
client MUST verify the identity of that resource server, as per
Section 3.1 of "HTTP Over TLS" [RFC2818]. Note that the client MUST
validate the TLS certificate chain when making these requests to
protected resources. Presenting the token to an unauthenticated and
unauthorized resource server or failing to validate the certificate
chain will allow adversaries to steal the token and gain unauthorized
access to protected resources.
7.4.3. Summary of Recommendations
7.4.3.1. Safeguard bearer tokens
Client implementations MUST ensure that bearer tokens are not leaked
to unintended parties, as they will be able to use them to gain
access to protected resources. This is the primary security
consideration when using bearer tokens and underlies all the more
specific recommendations that follow.
7.4.3.2. Validate TLS certificate chains
The client MUST validate the TLS certificate chain when making
requests to protected resources. Failing to do so may enable DNS
hijacking attacks to steal the token and gain unintended access.
7.4.3.3. Always use TLS (https)
Clients MUST always use TLS (https) or equivalent transport security
when making requests with bearer tokens. Failing to do so exposes
the token to numerous attacks that could give attackers unintended
access.
7.4.3.4. Don't store bearer tokens in HTTP cookies
Implementations MUST NOT store bearer tokens within cookies that can
be sent in the clear (which is the default transmission mode for
cookies). Implementations that do store bearer tokens in cookies
MUST take precautions against cross-site request forgery.
Hardt, et al. Expires 6 January 2021 [Page 48]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
7.4.3.5. Issue short-lived bearer tokens
Token servers SHOULD issue short-lived (one hour or less) bearer
tokens, particularly when issuing tokens to clients that run within a
web browser or other environments where information leakage may
occur. Using short-lived bearer tokens can reduce the impact of them
being leaked.
7.4.3.6. Issue scoped bearer tokens
Token servers SHOULD issue bearer tokens that contain an audience
restriction, scoping their use to the intended relying party or set
of relying parties.
7.4.3.7. Don't pass bearer tokens in page URLs
Bearer tokens MUST NOT be passed in page URLs (for example, as query
string parameters). Instead, bearer tokens SHOULD be passed in HTTP
message headers or message bodies for which confidentiality measures
are taken. Browsers, web servers, and other software may not
adequately secure URLs in the browser history, web server logs, and
other data structures. If bearer tokens are passed in page URLs,
attackers might be able to steal them from the history data, logs, or
other unsecured locations.
7.4.4. Token Replay Prevention
A sender-constrained access token scopes the applicability of an
access token to a certain sender. This sender is obliged to
demonstrate knowledge of a certain secret as prerequisite for the
acceptance of that token at the recipient (e.g., a resource server).
Authorization and resource servers SHOULD use mechanisms for sender-
constrained access tokens to prevent token replay as described in
Section 4.8.1.1.2 of [I-D.ietf-oauth-security-topics]. The use of
Mutual TLS for OAuth 2.0 [RFC8705] is RECOMMENDED.
It is RECOMMENDED to use end-to-end TLS. If TLS traffic needs to be
terminated at an intermediary, refer to Section 4.11 of
[I-D.ietf-oauth-security-topics] for further security advice.
Hardt, et al. Expires 6 January 2021 [Page 49]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
7.4.5. Access Token Privilege Restriction
The privileges associated with an access token SHOULD be restricted
to the minimum required for the particular application or use case.
This prevents clients from exceeding the privileges authorized by the
resource owner. It also prevents users from exceeding their
privileges authorized by the respective security policy. Privilege
restrictions also help to reduce the impact of access token leakage.
In particular, access tokens SHOULD be restricted to certain resource
servers (audience restriction), preferably to a single resource
server. To put this into effect, the authorization server associates
the access token with certain resource servers and every resource
server is obliged to verify, for every request, whether the access
token sent with that request was meant to be used for that particular
resource server. If not, the resource server MUST refuse to serve
the respective request. Clients and authorization servers MAY
utilize the parameters "scope" or "resource" as specified in this
document and [RFC8707], respectively, to determine the resource
server they want to access.
Additionally, access tokens SHOULD be restricted to certain resources
and actions on resource servers or resources. To put this into
effect, the authorization server associates the access token with the
respective resource and actions and every resource server is obliged
to verify, for every request, whether the access token sent with that
request was meant to be used for that particular action on the
particular resource. If not, the resource server must refuse to
serve the respective request. Clients and authorization servers MAY
utilize the parameter "scope" and "authorization_details" as
specified in [I-D.ietf-oauth-rar] to determine those resources and/or
actions.
8. Extensibility
8.1. Defining Access Token Types
Access token types can be defined in one of two ways: registered in
the Access Token Types registry (following the procedures in
Section 11.1 of [RFC6749]), or by using a unique absolute URI as its
name.
Types utilizing a URI name SHOULD be limited to vendor-specific
implementations that are not commonly applicable, and are specific to
the implementation details of the resource server where they are
used.
Hardt, et al. Expires 6 January 2021 [Page 50]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
All other types MUST be registered. Type names MUST conform to the
type-name ABNF. If the type definition includes a new HTTP
authentication scheme, the type name SHOULD be identical to the HTTP
authentication scheme name (as defined by [RFC2617]). The token type
"example" is reserved for use in examples.
type-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
8.2. Defining New Endpoint Parameters
New request or response parameters for use with the authorization
endpoint or the token endpoint are defined and registered in the
OAuth Parameters registry following the procedure in Section 11.2 of
[RFC6749].
Parameter names MUST conform to the param-name ABNF, and parameter
values syntax MUST be well-defined (e.g., using ABNF, or a reference
to the syntax of an existing parameter).
param-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
Unregistered vendor-specific parameter extensions that are not
commonly applicable and that are specific to the implementation
details of the authorization server where they are used SHOULD
utilize a vendor-specific prefix that is not likely to conflict with
other registered values (e.g., begin with 'companyname_').
8.3. Defining New Authorization Grant Types
New authorization grant types can be defined by assigning them a
unique absolute URI for use with the "grant_type" parameter. If the
extension grant type requires additional token endpoint parameters,
they MUST be registered in the OAuth Parameters registry as described
by Section 11.2 of [RFC6749].
8.4. Defining New Authorization Endpoint Response Types
New response types for use with the authorization endpoint are
defined and registered in the Authorization Endpoint Response Types
registry following the procedure in Section 11.3 of [RFC6749].
Response type names MUST conform to the response-type ABNF.
response-type = response-name *( SP response-name )
response-name = 1*response-char
response-char = "_" / DIGIT / ALPHA
Hardt, et al. Expires 6 January 2021 [Page 51]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
If a response type contains one or more space characters (%x20), it
is compared as a space-delimited list of values in which the order of
values does not matter. Only one order of values can be registered,
which covers all other arrangements of the same set of values.
For example, an extension can define and register the "code
other_token" response type. Once registered, the same combination
cannot be registered as "other_token code", but both values can be
used to denote the same response type.
8.5. Defining Additional Error Codes
In cases where protocol extensions (i.e., access token types,
extension parameters, or extension grant types) require additional
error codes to be used with the authorization code grant error
response (Section 4.1.2.1), the token error response (Section 5.2),
or the resource access error response (Section 7.3), such error codes
MAY be defined.
Extension error codes MUST be registered (following the procedures in
Section 11.4 of [RFC6749]) if the extension they are used in
conjunction with is a registered access token type, a registered
endpoint parameter, or an extension grant type. Error codes used
with unregistered extensions MAY be registered.
Error codes MUST conform to the error ABNF and SHOULD be prefixed by
an identifying name when possible. For example, an error identifying
an invalid value set to the extension parameter "example" SHOULD be
named "example_invalid".
error = 1*error-char
error-char = %x20-21 / %x23-5B / %x5D-7E
9. Security Considerations
As a flexible and extensible framework, OAuth's security
considerations depend on many factors. The following sections
provide implementers with security guidelines focused on the three
client profiles described in Section 2.1: web application, browser-
based application, and native application.
A comprehensive OAuth security model and analysis, as well as
background for the protocol design, is provided by [RFC6819] and
[I-D.ietf-oauth-security-topics].
Hardt, et al. Expires 6 January 2021 [Page 52]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
9.1. Client Authentication
Authorization servers SHOULD use client authentication if possible.
It is RECOMMENDED to use asymmetric (public-key based) methods for
client authentication such as mTLS [RFC8705] or "private_key_jwt"
[OpenID]. When asymmetric methods for client authentication are
used, authorization servers do not need to store sensitive symmetric
keys, making these methods more robust against a number of attacks.
Authorization server MUST only rely on client authentication if the
process of issuance/registration and distribution of the underlying
credentials ensures their confidentiality.
When client authentication is not possible, the authorization server
SHOULD employ other means to validate the client's identity - for
example, by requiring the registration of the client redirect URI or
enlisting the resource owner to confirm identity. A valid redirect
URI is not sufficient to verify the client's identity when asking for
resource owner authorization but can be used to prevent delivering
credentials to a counterfeit client after obtaining resource owner
authorization.
The authorization server must consider the security implications of
interacting with unauthenticated clients and take measures to limit
the potential exposure of other credentials (e.g., refresh tokens)
issued to such clients.
The privileges an authorization server associates with a certain
client identity MUST depend on the assessment of the overall process
for client identification and client credential lifecycle management.
For example, authentication of a dynamically registered client just
ensures the authorization server it is talking to the same client
again. In contrast, if there is a web application whose developer's
identity was verified, who signed a contract and is issued a client
secret that is only used in a secure backend service, the
authorization server might allow this client to access more sensible
services or to use the client credential grant type.
9.1.1. Client Authentication of Native Apps
Secrets that are statically included as part of an app distributed to
multiple users should not be treated as confidential secrets, as one
user may inspect their copy and learn the shared secret. For this
reason, it is NOT RECOMMENDED for authorization servers to require
client authentication of public native apps clients using a shared
secret, as this serves little value beyond client identification
which is already provided by the "client_id" request parameter.
Hardt, et al. Expires 6 January 2021 [Page 53]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
Authorization servers that still require a statically included shared
secret for native app clients MUST treat the client as a public
client (as defined in Section 2.1), and not accept the secret as
proof of the client's identity. Without additional measures, such
clients are subject to client impersonation (see Section 9.3.1).
9.2. Registration of Native App Clients
Except when using a mechanism like Dynamic Client Registration
[RFC7591] to provision per-instance secrets, native apps are
classified as public clients, as defined in Section 2.1; they MUST be
registered with the authorization server as such. Authorization
servers MUST record the client type in the client registration
details in order to identify and process requests accordingly.
Authorization servers MUST require clients to register their complete
redirect URI (including the path component) and reject authorization
requests that specify a redirect URI that doesn't exactly match the
one that was registered; the exception is loopback redirects, where
an exact match is required except for the port URI component.
For private-use URI scheme-based redirects, authorization servers
SHOULD enforce the requirement in Section 10.3.1 that clients use
schemes that are reverse domain name based. At a minimum, any
private-use URI scheme that doesn't contain a period character (".")
SHOULD be rejected.
In addition to the collision-resistant properties, requiring a URI
scheme based on a domain name that is under the control of the app
can help to prove ownership in the event of a dispute where two apps
claim the same private-use URI scheme (where one app is acting
maliciously). For example, if two apps claimed "com.example.app",
the owner of "example.com" could petition the app store operator to
remove the counterfeit app. Such a petition is harder to prove if a
generic URI scheme was used.
Authorization servers MAY request the inclusion of other platform-
specific information, such as the app package or bundle name, or
other information that may be useful for verifying the calling app's
identity on operating systems that support such functions.
9.3. Client Impersonation
A malicious client can impersonate another client and obtain access
to protected resources if the impersonated client fails to, or is
unable to, keep its client credentials confidential.
Hardt, et al. Expires 6 January 2021 [Page 54]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
The authorization server MUST authenticate the client whenever
possible. If the authorization server cannot authenticate the client
due to the client's nature, the authorization server MUST require the
registration of any redirect URI used for receiving authorization
responses and SHOULD utilize other means to protect resource owners
from such potentially malicious clients. For example, the
authorization server can engage the resource owner to assist in
identifying the client and its origin.
The authorization server SHOULD enforce explicit resource owner
authentication and provide the resource owner with information about
the client and the requested authorization scope and lifetime. It is
up to the resource owner to review the information in the context of
the current client and to authorize or deny the request.
The authorization server SHOULD NOT process repeated authorization
requests automatically (without active resource owner interaction)
without authenticating the client or relying on other measures to
ensure that the repeated request comes from the original client and
not an impersonator.
9.3.1. Impersonation of Native Apps
As stated above, the authorization server SHOULD NOT process
authorization requests automatically without user consent or
interaction, except when the identity of the client can be assured.
This includes the case where the user has previously approved an
authorization request for a given client id - unless the identity of
the client can be proven, the request SHOULD be processed as if no
previous request had been approved.
Measures such as claimed "https" scheme redirects MAY be accepted by
authorization servers as identity proof. Some operating systems may
offer alternative platform-specific identity features that MAY be
accepted, as appropriate.
9.4. Access Tokens
Access token credentials (as well as any confidential access token
attributes) MUST be kept confidential in transit and storage, and
only shared among the authorization server, the resource servers the
access token is valid for, and the client to whom the access token is
issued. Access token credentials MUST only be transmitted using TLS
as described in Section 1.6 with server authentication as defined by
[RFC2818].
Hardt, et al. Expires 6 January 2021 [Page 55]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
The authorization server MUST ensure that access tokens cannot be
generated, modified, or guessed to produce valid access tokens by
unauthorized parties.
9.4.1. Access Token Privilege Restriction
The client SHOULD request access tokens with the minimal scope
necessary. The authorization server SHOULD take the client identity
into account when choosing how to honor the requested scope and MAY
issue an access token with less rights than requested.
The privileges associated with an access token SHOULD be restricted
to the minimum required for the particular application or use case.
This prevents clients from exceeding the privileges authorized by the
resource owner. It also prevents users from exceeding their
privileges authorized by the respective security policy. Privilege
restrictions also help to reduce the impact of access token leakage.
In particular, access tokens SHOULD be restricted to certain resource
servers (audience restriction), preferably to a single resource
server. To put this into effect, the authorization server associates
the access token with certain resource servers and every resource
server is obliged to verify, for every request, whether the access
token sent with that request was meant to be used for that particular
resource server. If not, the resource server MUST refuse to serve
the respective request. Clients and authorization servers MAY
utilize the parameters "scope" or "resource" as specified in
[RFC8707], respectively, to determine the resource server they want
to access.
9.4.2. Access Token Replay Prevention
Additionally, access tokens SHOULD be restricted to certain resources
and actions on resource servers or resources. To put this into
effect, the authorization server associates the access token with the
respective resource and actions and every resource server is obliged
to verify, for every request, whether the access token sent with that
request was meant to be used for that particular action on the
particular resource. If not, the resource server must refuse to
serve the respective request. Clients and authorization servers MAY
utilize the parameter "scope" and "authorization_details" as
specified in [I-D.ietf-oauth-rar] to determine those resources and/or
actions.
Authorization and resource servers SHOULD use mechanisms for sender-
constrained access tokens to prevent token replay as described in
(#pop_tokens). A sender-constrained access token scopes the
applicability of an access token to a certain sender. This sender is
Hardt, et al. Expires 6 January 2021 [Page 56]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
obliged to demonstrate knowledge of a certain secret as prerequisite
for the acceptance of that token at the recipient (e.g., a resource
server). The use of Mutual TLS for OAuth 2.0 [RFC8705] is
RECOMMENDED.
9.5. Refresh Tokens
Authorization servers MAY issue refresh tokens to clients.
Refresh tokens MUST be kept confidential in transit and storage, and
shared only among the authorization server and the client to whom the
refresh tokens were issued. The authorization server MUST maintain
the binding between a refresh token and the client to whom it was
issued. Refresh tokens MUST only be transmitted using TLS as
described in Section 1.6 with server authentication as defined by
[RFC2818].
The authorization server MUST verify the binding between the refresh
token and client identity whenever the client identity can be
authenticated. When client authentication is not possible, the
authorization server SHOULD issue sender-constrained refresh tokens
or use refresh token rotation as described in
(#refresh_token_protection).
The authorization server MUST ensure that refresh tokens cannot be
generated, modified, or guessed to produce valid refresh tokens by
unauthorized parties.
9.6. Client Impersonating Resource Owner
Resource servers may make access control decisions based on the
identity of the resource owner as communicated in the "sub" claim
returned by the authorization server in a token introspection
response [RFC7662] or other mechanisms. If a client is able to
choose its own "client_id" during registration with the authorization
server, then there is a risk that it can register with the same "sub"
value as a privileged user. A subsequent access token obtained under
the client credentials grant may be mistaken for an access token
authorized by the privileged user if the resource server does not
perform additional checks.
Authorization servers SHOULD NOT allow clients to influence their
"client_id" or "sub" value or any other claim if that can cause
confusion with a genuine resource owner. Where this cannot be
avoided, authorization servers MUST provide other means for the
resource server to distinguish between access tokens authorized by a
resource owner from access tokens authorized by the client itself.
Hardt, et al. Expires 6 January 2021 [Page 57]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
9.7. Protecting Redirect-Based Flows
When comparing client redirect URIs against pre-registered URIs,
authorization servers MUST utilize exact string matching. This
measure contributes to the prevention of leakage of authorization
codes and access tokens (see (#insufficient_uri_validation)). It can
also help to detect mix-up attacks (see (#mix_up)).
Clients MUST NOT expose URLs that forward the user's browser to
arbitrary URIs obtained from a query parameter ("open redirector").
Open redirectors can enable exfiltration of authorization codes and
access tokens, see (#open_redirector_on_client).
Clients MUST prevent Cross-Site Request Forgery (CSRF). In this
context, CSRF refers to requests to the redirection endpoint that do
not originate at the authorization server, but a malicious third
party (see Section 4.4.1.8. of [RFC6819] for details). Clients that
have ensured that the authorization server supports the
"code_challenge" parameter MAY rely the CSRF protection provided by
that mechanism. In OpenID Connect flows, the "nonce" parameter
provides CSRF protection. Otherwise, one-time use CSRF tokens
carried in the "state" parameter that are securely bound to the user
agent MUST be used for CSRF protection (see (#csrf_countermeasures)).
In order to prevent mix-up attacks (see (#mix_up)), clients MUST only
process redirect responses of the authorization server they sent the
respective request to and from the same user agent this authorization
request was initiated with. Clients MUST store the authorization
server they sent an authorization request to and bind this
information to the user agent and check that the authorization
request was received from the correct authorization server. Clients
MUST ensure that the subsequent token request, if applicable, is sent
to the same authorization server. Clients SHOULD use distinct
redirect URIs for each authorization server as a means to identify
the authorization server a particular response came from.
An AS that redirects a request potentially containing user
credentials MUST avoid forwarding these user credentials accidentally
(see Section 9.7.2 for details).
9.7.1. Loopback Redirect Considerations in Native Apps
Loopback interface redirect URIs use the "http" scheme (i.e., without
Transport Layer Security (TLS)). This is acceptable for loopback
interface redirect URIs as the HTTP request never leaves the device.
Clients should open the network port only when starting the
authorization request and close it once the response is returned.
Hardt, et al. Expires 6 January 2021 [Page 58]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
Clients should listen on the loopback network interface only, in
order to avoid interference by other network actors.
While redirect URIs using localhost (i.e.,
"http://localhost:{port}/{path}") function similarly to loopback IP
redirects described in Section 10.3.3, the use of "localhost" is NOT
RECOMMENDED. Specifying a redirect URI with the loopback IP literal
rather than "localhost" avoids inadvertently listening on network
interfaces other than the loopback interface. It is also less
susceptible to client-side firewalls and misconfigured host name
resolution on the user's device.
9.7.2. HTTP 307 Redirect
An AS which redirects a request that potentially contains user
credentials MUST NOT use the HTTP 307 status code for redirection.
If an HTTP redirection (and not, for example, JavaScript) is used for
such a request, AS SHOULD use HTTP status code 303 "See Other".
At the authorization endpoint, a typical protocol flow is that the AS
prompts the user to enter her credentials in a form that is then
submitted (using the HTTP POST method) back to the authorization
server. The AS checks the credentials and, if successful, redirects
the user agent to the client's redirect URI.
If the status code 307 were used for redirection, the user agent
would send the user credentials via HTTP POST to the client.
This discloses the sensitive credentials to the client. If the
relying party is malicious, it can use the credentials to impersonate
the user at the AS.
The behavior might be unexpected for developers, but is defined in
[RFC7231], Section 6.4.7. This status code does not require the user
agent to rewrite the POST request to a GET request and thereby drop
the form data in the POST request body.
In the HTTP standard [RFC7231], only the status code 303
unambigiously enforces rewriting the HTTP POST request to an HTTP GET
request. For all other status codes, including the popular 302, user
agents can opt not to rewrite POST to GET requests and therefore to
reveal the user credentials to the client. (In practice, however,
most user agents will only show this behaviour for 307 redirects.)
Therefore, the RECOMMENDED status code for HTTP redirects is 303.
Hardt, et al. Expires 6 January 2021 [Page 59]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
9.8. Authorization Codes
The transmission of authorization codes MUST be made over a secure
channel, and the client MUST require the use of TLS with its redirect
URI if the URI identifies a network resource. Since authorization
codes are transmitted via user-agent redirections, they could
potentially be disclosed through user-agent history and HTTP referrer
headers.
Authorization codes MUST be short lived and single-use. If the
authorization server observes multiple attempts to exchange an
authorization code for an access token, the authorization server
SHOULD attempt to revoke all refresh and access tokens already
granted based on the compromised authorization code.
If the client can be authenticated, the authorization servers MUST
authenticate the client and ensure that the authorization code was
issued to the same client.
Clients MUST prevent injection (replay) of authorization codes into
the authorization response by attackers. To this end, using
"code_challenge" and "code_verifier" is REQUIRED for clients and
authorization servers MUST enforce their use, unless both of the
following criteria are met:
* The client is a confidential or credentialed client.
* In the specific deployment and the specific request, there is
reasonable assurance for authorization server that the client
implements the OpenID Connect "nonce" mechanism properly.
In this case, using and enforcing "code_challenge" and
"code_verifier" is still RECOMMENDED.
The "code_challenge" or OpenID Connect "nonce" value MUST be
transaction-specific and securely bound to the client and the user
agent in which the transaction was started. If a transaction leads
to an error, fresh values for "code_challenge" or "nonce" MUST be
chosen.
Historic note: Although PKCE [RFC7636] was originally designed as a
mechanism to protect native apps, this advice applies to all kinds of
OAuth clients, including web applications and other confidential
clients.
Hardt, et al. Expires 6 January 2021 [Page 60]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
Clients SHOULD use code challenge methods that do not expose the
"code_verifier" in the authorization request. Otherwise, attackers
that can read the authorization request (cf. Attacker A4 in
(#secmodel)) can break the security provided by this mechanism.
Currently, "S256" is the only such method.
When an authorization code arrives at the token endpoint, the
authorization server MUST do the following check:
1. If there was a "code_challenge" in the authorization request for
which this code was issued, there must be a "code_verifier" in
the token request, and it MUST be verified according to the steps
in Section 4.1.3. (This is no change from the current behavior
in [RFC7636].)
2. If there was no "code_challenge" in the authorization request,
any request to the token endpoint containing a "code_verifier"
MUST be rejected.
Authorization servers MUST support the "code_challenge" and
"code_verifier" parameters.
Authorization servers MUST provide a way to detect their support for
the "code_challenge" mechanism. To this end, they MUST either (a)
publish the element "code_challenge_methods_supported" in their AS
metadata ([RFC8414]) containing the supported
"code_challenge_method"s (which can be used by the client to detect
support) or (b) provide a deployment-specific way to ensure or
determine support by the AS.
9.9. Request Confidentiality
Access tokens, refresh tokens, authorization codes, and client
credentials MUST NOT be transmitted in the clear.
The "state" and "scope" parameters SHOULD NOT include sensitive
client or resource owner information in plain text, as they can be
transmitted over insecure channels or stored insecurely.
9.10. Ensuring Endpoint Authenticity
In order to prevent man-in-the-middle attacks, the authorization
server MUST require the use of TLS with server authentication as
defined by [RFC2818] for any request sent to the authorization and
token endpoints. The client MUST validate the authorization server's
TLS certificate as defined by [RFC6125] and in accordance with its
requirements for server identity authentication.
Hardt, et al. Expires 6 January 2021 [Page 61]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
9.11. Credentials-Guessing Attacks
The authorization server MUST prevent attackers from guessing access
tokens, authorization codes, refresh tokens, resource owner
passwords, and client credentials.
The probability of an attacker guessing generated tokens (and other
credentials not intended for handling by end-users) MUST be less than
or equal to 2^(-128) and SHOULD be less than or equal to 2^(-160).
The authorization server MUST utilize other means to protect
credentials intended for end-user usage.
9.12. Phishing Attacks
Wide deployment of this and similar protocols may cause end-users to
become inured to the practice of being redirected to websites where
they are asked to enter their passwords. If end-users are not
careful to verify the authenticity of these websites before entering
their credentials, it will be possible for attackers to exploit this
practice to steal resource owners' passwords.
Service providers should attempt to educate end-users about the risks
phishing attacks pose and should provide mechanisms that make it easy
for end-users to confirm the authenticity of their sites. Client
developers should consider the security implications of how they
interact with the user-agent (e.g., external, embedded), and the
ability of the end-user to verify the authenticity of the
authorization server.
To reduce the risk of phishing attacks, the authorization servers
MUST require the use of TLS on every endpoint used for end-user
interaction.
9.13. Fake External User-Agents in Native Apps
The native app that is initiating the authorization request has a
large degree of control over the user interface and can potentially
present a fake external user-agent, that is, an embedded user-agent
made to appear as an external user-agent.
When all good actors are using external user-agents, the advantage is
that it is possible for security experts to detect bad actors, as
anyone faking an external user-agent is provably bad. On the other
hand, if good and bad actors alike are using embedded user-agents,
bad actors don't need to fake anything, making them harder to detect.
Once a malicious app is detected, it may be possible to use this
knowledge to blacklist the app's signature in malware scanning
Hardt, et al. Expires 6 January 2021 [Page 62]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
software, take removal action (in the case of apps distributed by app
stores) and other steps to reduce the impact and spread of the
malicious app.
Authorization servers can also directly protect against fake external
user-agents by requiring an authentication factor only available to
true external user-agents.
Users who are particularly concerned about their security when using
in-app browser tabs may also take the additional step of opening the
request in the full browser from the in-app browser tab and complete
the authorization there, as most implementations of the in-app
browser tab pattern offer such functionality.
9.14. Malicious External User-Agents in Native Apps
If a malicious app is able to configure itself as the default handler
for "https" scheme URIs in the operating system, it will be able to
intercept authorization requests that use the default browser and
abuse this position of trust for malicious ends such as phishing the
user.
This attack is not confined to OAuth; a malicious app configured in
this way would present a general and ongoing risk to the user beyond
OAuth usage by native apps. Many operating systems mitigate this
issue by requiring an explicit user action to change the default
handler for "http" and "https" scheme URIs.
9.15. Cross-Site Request Forgery
An attacker might attempt to inject a request to the redirect URI of
the legitimate client on the victim's device, e.g., to cause the
client to access resources under the attacker's control. This is a
variant of an attack known as Cross-Site Request Forgery (CSRF).
The traditional countermeasure are CSRF tokens that are bound to the
user agent and passed in the "state" parameter to the authorization
server as described in [RFC6819]. The same protection is provided by
the "code_verifier" parameter or the OpenID Connect "nonce" value.
When using "code_verifier" instead of "state" or "nonce" for CSRF
protection, it is important to note that:
* Clients MUST ensure that the AS supports the
"code_challenge_method" intended to be used by the client. If an
authorization server does not support the requested method,
"state" or "nonce" MUST be used for CSRF protection instead.
Hardt, et al. Expires 6 January 2021 [Page 63]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
* If "state" is used for carrying application state, and integrity
of its contents is a concern, clients MUST protect "state" against
tampering and swapping. This can be achieved by binding the
contents of state to the browser session and/or signed/encrypted
state values [I-D.bradley-oauth-jwt-encoded-state].
AS therefore MUST provide a way to detect their supported code
challenge methods either via AS metadata according to [RFC8414] or
provide a deployment-specific way to ensure or determine support.
9.16. Clickjacking
As described in Section 4.4.1.9 of [RFC6819], the authorization
request is susceptible to clickjacking. An attacker can use this
vector to obtain the user's authentication credentials, change the
scope of access granted to the client, and potentially access the
user's resources.
Authorization servers MUST prevent clickjacking attacks. Multiple
countermeasures are described in [RFC6819], including the use of the
X-Frame-Options HTTP response header field and frame-busting
JavaScript. In addition to those, authorization servers SHOULD also
use Content Security Policy (CSP) level 2 [CSP-2] or greater.
To be effective, CSP must be used on the authorization endpoint and,
if applicable, other endpoints used to authenticate the user and
authorize the client (e.g., the device authorization endpoint, login
pages, error pages, etc.). This prevents framing by unauthorized
origins in user agents that support CSP. The client MAY permit being
framed by some other origin than the one used in its redirection
endpoint. For this reason, authorization servers SHOULD allow
administrators to configure allowed origins for particular clients
and/or for clients to register these dynamically.
Using CSP allows authorization servers to specify multiple origins in
a single response header field and to constrain these using flexible
patterns (see [CSP-2] for details). Level 2 of this standard
provides a robust mechanism for protecting against clickjacking by
using policies that restrict the origin of frames (using "frame-
ancestors") together with those that restrict the sources of scripts
allowed to execute on an HTML page (by using "script-src"). A non-
normative example of such a policy is shown in the following listing:
"HTTP/1.1 200 OK Content-Security-Policy: frame-ancestors
https://ext.example.org:8000 Content-Security-Policy: script-src
'self' X-Frame-Options: ALLOW-FROM https://ext.example.org:8000 ..."
Hardt, et al. Expires 6 January 2021 [Page 64]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
Because some user agents do not support [CSP-2], this technique
SHOULD be combined with others, including those described in
[RFC6819], unless such legacy user agents are explicitly unsupported
by the authorization server. Even in such cases, additional
countermeasures SHOULD still be employed.
9.17. Code Injection and Input Validation
A code injection attack occurs when an input or otherwise external
variable is used by an application unsanitized and causes
modification to the application logic. This may allow an attacker to
gain access to the application device or its data, cause denial of
service, or introduce a wide range of malicious side-effects.
The authorization server and client MUST sanitize (and validate when
possible) any value received - in particular, the value of the
"state" and "redirect_uri" parameters.
9.18. Open Redirectors
The following attacks can occur when an AS or client has an open
redirector. An open redirector is an endpoint that forwards a user's
browser to an arbitrary URI obtained from a query parameter.
9.18.1. Client as Open Redirector
Clients MUST NOT expose open redirectors. Attackers may use open
redirectors to produce URLs pointing to the client and utilize them
to exfiltrate authorization codes and access tokens, as described in
(#redir_uri_open_redir). Another abuse case is to produce URLs that
appear to point to the client. This might trick users into trusting
the URL and follow it in their browser. This can be abused for
phishing.
In order to prevent open redirection, clients should only redirect if
the target URLs are whitelisted or if the origin and integrity of a
request can be authenticated. Countermeasures against open
redirection are described by OWASP [owasp_redir].
9.18.2. Authorization Server as Open Redirector
Just as with clients, attackers could try to utilize a user's trust
in the authorization server (and its URL in particular) for
performing phishing attacks. OAuth authorization servers regularly
redirect users to other web sites (the clients), but must do so in a
safe way.
Hardt, et al. Expires 6 January 2021 [Page 65]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
Section 4.1.2.1 already prevents open redirects by stating that the
AS MUST NOT automatically redirect the user agent in case of an
invalid combination of "client_id" and "redirect_uri".
However, an attacker could also utilize a correctly registered
redirect URI to perform phishing attacks. The attacker could, for
example, register a client via dynamic client registration [RFC7591]
and intentionally send an erroneous authorization request, e.g., by
using an invalid scope value, thus instructing the AS to redirect the
user agent to its phishing site.
The AS MUST take precautions to prevent this threat. Based on its
risk assessment, the AS needs to decide whether it can trust the
redirect URI and SHOULD only automatically redirect the user agent if
it trusts the redirect URI. If the URI is not trusted, the AS MAY
inform the user and rely on the user to make the correct decision.
9.19. Authorization Server Mix-Up Mitigation in Native Apps
(TODO: merge this with the regular mix-up section when it is brought
in)
To protect against a compromised or malicious authorization server
attacking another authorization server used by the same app, it is
REQUIRED that a unique redirect URI is used for each authorization
server used by the app (for example, by varying the path component),
and that authorization responses are rejected if the redirect URI
they were received on doesn't match the redirect URI in an outgoing
authorization request.
The native app MUST store the redirect URI used in the authorization
request with the authorization session data (i.e., along with "state"
and other related data) and MUST verify that the URI on which the
authorization response was received exactly matches it.
The requirement of Section 9.2, specifically that authorization
servers reject requests with URIs that don't match what was
registered, is also required to prevent such attacks.
9.20. Embedded User Agents in Native Apps
Embedded user-agents are a technically possible method for
authorizing native apps. These embedded user-agents are unsafe for
use by third parties to the authorization server by definition, as
the app that hosts the embedded user-agent can access the user's full
authentication credential, not just the OAuth authorization grant
that was intended for the app.
Hardt, et al. Expires 6 January 2021 [Page 66]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
In typical web-view-based implementations of embedded user-agents,
the host application can record every keystroke entered in the login
form to capture usernames and passwords, automatically submit forms
to bypass user consent, and copy session cookies and use them to
perform authenticated actions as the user.
Even when used by trusted apps belonging to the same party as the
authorization server, embedded user-agents violate the principle of
least privilege by having access to more powerful credentials than
they need, potentially increasing the attack surface.
Encouraging users to enter credentials in an embedded user-agent
without the usual address bar and visible certificate validation
features that browsers have makes it impossible for the user to know
if they are signing in to the legitimate site; even when they are, it
trains them that it's OK to enter credentials without validating the
site first.
Aside from the security concerns, embedded user-agents do not share
the authentication state with other apps or the browser, requiring
the user to log in for every authorization request, which is often
considered an inferior user experience.
9.21. Other Recommendations
Authorization servers SHOULD NOT allow clients to influence their
"client_id" or "sub" value or any other claim if that can cause
confusion with a genuine resource owner (see
(#client_impersonating)).
10. Native Applications
Native applications are clients installed and executed on the device
used by the resource owner (i.e., desktop application, native mobile
application). Native applications require special consideration
related to security, platform capabilities, and overall end-user
experience.
The authorization endpoint requires interaction between the client
and the resource owner's user-agent. The best current practice is to
perform the OAuth authorization request in an external user-agent
(typically the browser) rather than an embedded user-agent (such as
one implemented with web-views).
The native application can capture the response from the
authorization server using a redirect URI with a scheme registered
with the operating system to invoke the client as the handler, manual
copy-and-paste of the credentials, running a local web server,
Hardt, et al. Expires 6 January 2021 [Page 67]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
installing a user-agent extension, or by providing a redirect URI
identifying a server-hosted resource under the client's control,
which in turn makes the response available to the native application.
Previously, it was common for native apps to use embedded user-agents
(commonly implemented with web-views) for OAuth authorization
requests. That approach has many drawbacks, including the host app
being able to copy user credentials and cookies as well as the user
needing to authenticate from scratch in each app. See Section 9.20
for a deeper analysis of the drawbacks of using embedded user-agents
for OAuth.
Native app authorization requests that use the browser are more
secure and can take advantage of the user's authentication state.
Being able to use the existing authentication session in the browser
enables single sign-on, as users don't need to authenticate to the
authorization server each time they use a new app (unless required by
the authorization server policy).
Supporting authorization flows between a native app and the browser
is possible without changing the OAuth protocol itself, as the OAuth
authorization request and response are already defined in terms of
URIs. This encompasses URIs that can be used for inter-app
communication. Some OAuth server implementations that assume all
clients are confidential web clients will need to add an
understanding of public native app clients and the types of redirect
URIs they use to support this best practice.
10.1. Using Inter-App URI Communication for OAuth in Native Apps
Just as URIs are used for OAuth on the web to initiate the
authorization request and return the authorization response to the
requesting website, URIs can be used by native apps to initiate the
authorization request in the device's browser and return the response
to the requesting native app.
By adopting the same methods used on the web for OAuth, benefits seen
in the web context like the usability of a single sign-on session and
the security of a separate authentication context are likewise gained
in the native app context. Reusing the same approach also reduces
the implementation complexity and increases interoperability by
relying on standards-based web flows that are not specific to a
particular platform.
Hardt, et al. Expires 6 January 2021 [Page 68]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
Native apps MUST use an external user-agent to perform OAuth
authorization requests. This is achieved by opening the
authorization request in the browser (detailed in Section 10.2) and
using a redirect URI that will return the authorization response back
to the native app (defined in Section 10.3).
10.2. Initiating the Authorization Request from a Native App
Native apps needing user authorization create an authorization
request URI with the authorization code grant type per Section 4.1
using a redirect URI capable of being received by the native app.
The function of the redirect URI for a native app authorization
request is similar to that of a web-based authorization request.
Rather than returning the authorization response to the OAuth
client's server, the redirect URI used by a native app returns the
response to the app. Several options for a redirect URI that will
return the authorization response to the native app in different
platforms are documented in Section 10.3. Any redirect URI that
allows the app to receive the URI and inspect its parameters is
viable.
After constructing the authorization request URI, the app uses
platform-specific APIs to open the URI in an external user-agent.
Typically, the external user-agent used is the default browser, that
is, the application configured for handling "http" and "https" scheme
URIs on the system; however, different browser selection criteria and
other categories of external user-agents MAY be used.
This best practice focuses on the browser as the RECOMMENDED external
user-agent for native apps. An external user-agent designed
specifically for user authorization and capable of processing
authorization requests and responses like a browser MAY also be used.
Other external user-agents, such as a native app provided by the
authorization server may meet the criteria set out in this best
practice, including using the same redirect URI properties, but their
use is out of scope for this specification.
Some platforms support a browser feature known as "in-app browser
tabs", where an app can present a tab of the browser within the app
context without switching apps, but still retain key benefits of the
browser such as a shared authentication state and security context.
On platforms where they are supported, it is RECOMMENDED, for
usability reasons, that apps use in-app browser tabs for the
authorization request.
Hardt, et al. Expires 6 January 2021 [Page 69]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
10.3. Receiving the Authorization Response in a Native App
There are several redirect URI options available to native apps for
receiving the authorization response from the browser, the
availability and user experience of which varies by platform.
To fully support native apps, authorization servers MUST offer at
least the three redirect URI options described in the following
subsections to native apps. Native apps MAY use whichever redirect
option suits their needs best, taking into account platform-specific
implementation details.
10.3.1. Private-Use URI Scheme Redirection
Many mobile and desktop computing platforms support inter-app
communication via URIs by allowing apps to register private-use URI
schemes (sometimes colloquially referred to as "custom URL schemes")
like "com.example.app". When the browser or another app attempts to
load a URI with a private-use URI scheme, the app that registered it
is launched to handle the request.
To perform an authorization request with a private-use URI scheme
redirect, the native app launches the browser with a standard
authorization request, but one where the redirect URI utilizes a
private-use URI scheme it registered with the operating system.
When choosing a URI scheme to associate with the app, apps MUST use a
URI scheme based on a domain name under their control, expressed in
reverse order, as recommended by Section 3.8 of [RFC7595] for
private-use URI schemes.
For example, an app that controls the domain name "app.example.com"
can use "com.example.app" as their scheme. Some authorization
servers assign client identifiers based on domain names, for example,
"client1234.usercontent.example.net", which can also be used as the
domain name for the scheme when reversed in the same manner. A
scheme such as "myapp", however, would not meet this requirement, as
it is not based on a domain name.
When there are multiple apps by the same publisher, care must be
taken so that each scheme is unique within that group. On platforms
that use app identifiers based on reverse-order domain names, those
identifiers can be reused as the private-use URI scheme for the OAuth
redirect to help avoid this problem.
Hardt, et al. Expires 6 January 2021 [Page 70]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
Following the requirements of Section 3.2 of [RFC3986], as there is
no naming authority for private-use URI scheme redirects, only a
single slash ("/") appears after the scheme component. A complete
example of a redirect URI utilizing a private-use URI scheme is:
com.example.app:/oauth2redirect/example-provider
When the authorization server completes the request, it redirects to
the client's redirect URI as it would normally. As the redirect URI
uses a private-use URI scheme, it results in the operating system
launching the native app, passing in the URI as a launch parameter.
Then, the native app uses normal processing for the authorization
response.
10.3.2. Claimed "https" Scheme URI Redirection
Some operating systems allow apps to claim "https" scheme [RFC7230]
URIs in the domains they control. When the browser encounters a
claimed URI, instead of the page being loaded in the browser, the
native app is launched with the URI supplied as a launch parameter.
Such URIs can be used as redirect URIs by native apps. They are
indistinguishable to the authorization server from a regular web-
based client redirect URI. An example is:
https://app.example.com/oauth2redirect/example-provider
As the redirect URI alone is not enough to distinguish public native
app clients from confidential web clients, it is REQUIRED in
Section 9.2 that the client type be recorded during client
registration to enable the server to determine the client type and
act accordingly.
App-claimed "https" scheme redirect URIs have some advantages
compared to other native app redirect options in that the identity of
the destination app is guaranteed to the authorization server by the
operating system. For this reason, native apps SHOULD use them over
the other options where possible.
10.3.3. Loopback Interface Redirection
Native apps that are able to open a port on the loopback network
interface without needing special permissions (typically, those on
desktop operating systems) can use the loopback interface to receive
the OAuth redirect.
Loopback redirect URIs use the "http" scheme and are constructed with
the loopback IP literal and whatever port the client is listening on.
Hardt, et al. Expires 6 January 2021 [Page 71]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
That is, "http://127.0.0.1:{port}/{path}" for IPv4, and
"http://[::1]:{port}/{path}" for IPv6. An example redirect using the
IPv4 loopback interface with a randomly assigned port:
http://127.0.0.1:51004/oauth2redirect/example-provider
An example redirect using the IPv6 loopback interface with a randomly
assigned port:
http://[::1]:61023/oauth2redirect/example-provider
The authorization server MUST allow any port to be specified at the
time of the request for loopback IP redirect URIs, to accommodate
clients that obtain an available ephemeral port from the operating
system at the time of the request.
Clients SHOULD NOT assume that the device supports a particular
version of the Internet Protocol. It is RECOMMENDED that clients
attempt to bind to the loopback interface using both IPv4 and IPv6
and use whichever is available.
11. Browser-Based Apps
Browser-based apps are are clients that run in a web browser,
typically written in JavaScript, also known as "single-page apps".
These types of apps have particular security considerations similar
to native apps.
TODO: Bring in the normative text of the browser-based apps BCP when
it is finalized.
12. Differences from OAuth 2.0
This draft consolidates the functionality in OAuth 2.0 [RFC6749],
OAuth 2.0 for Native Apps ([RFC8252]), Proof Key for Code Exchange
([RFC7636]), OAuth 2.0 for Browser-Based Apps
([I-D.ietf-oauth-browser-based-apps]), OAuth Security Best Current
Practice ([I-D.ietf-oauth-security-topics]), and Bearer Token Usage
([RFC6750]).
Where a later draft updates or obsoletes functionality found in the
original [RFC6749], that functionality in this draft is updated with
the normative changes described in a later draft, or removed
entirely.
A non-normative list of changes from OAuth 2.0 is listed below:
Hardt, et al. Expires 6 January 2021 [Page 72]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
* The authorization code grant is extended with the functionality
from PKCE ([RFC7636]) such that the default method of using the
authorization code grant according to this specification requires
the addition of the PKCE parameters
* Redirect URIs must be compared using exact string matching as per
Section 4.1.3 of [I-D.ietf-oauth-security-topics]
* The Implicit grant ("response_type=token") is omitted from this
specification as per Section 2.1.2 of
[I-D.ietf-oauth-security-topics]
* The Resource Owner Password Credentials grant is omitted from this
specification as per Section 2.4 of
[I-D.ietf-oauth-security-topics]
* Bearer token usage omits the use of bearer tokens in the query
string of URIs as per Section 4.3.2 of
[I-D.ietf-oauth-security-topics]
* Refresh tokens should either be sender-constrained or one-time use
as per Section 4.12.2 of [I-D.ietf-oauth-security-topics]
13. IANA Considerations
This document does not require any IANA actions.
All referenced registries are defined by RFC6749 and related
documents that this work is based upon. No changes to those
registries are required by this specification.
14. References
14.1. Normative References
[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-15, 5 April 2020, <http://www.ietf.org/internet-
drafts/draft-ietf-oauth-security-topics-15.txt>.
[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/info/rfc2119>.
Hardt, et al. Expires 6 January 2021 [Page 73]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, DOI 10.17487/RFC2617, June 1999,
<https://www.rfc-editor.org/info/rfc2617>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
[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/info/rfc3986>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>.
Hardt, et al. Expires 6 January 2021 [Page 74]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
[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/info/rfc6750>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <https://www.rfc-editor.org/info/rfc7159>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014,
<https://www.rfc-editor.org/info/rfc7234>.
[RFC7595] Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines
and Registration Procedures for URI Schemes", BCP 35,
RFC 7595, DOI 10.17487/RFC7595, June 2015,
<https://www.rfc-editor.org/info/rfc7595>.
[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/info/rfc8174>.
[RFC8252] Denniss, W. and J. Bradley, "OAuth 2.0 for Native Apps",
BCP 212, RFC 8252, DOI 10.17487/RFC8252, October 2017,
<https://www.rfc-editor.org/info/rfc8252>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[USASCII] Institute, A.N.S., "Coded Character Set -- 7-bit American
Standard Code for Information Interchange, ANSI X3.4",
1986.
[W3C.REC-html401-19991224]
Raggett, D., Hors, A., and I. Jacobs, "HTML 4.01
Specification", World Wide Web Consortium Recommendation
REC-html401-19991224, 24 December 1999,
<http://www.w3.org/TR/1999/REC-html401-19991224>.
Hardt, et al. Expires 6 January 2021 [Page 75]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
[W3C.REC-xml-20081126]
Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20081126, 26 November 2008,
<http://www.w3.org/TR/2008/REC-xml-20081126>.
14.2. Informative References
[CSP-2] "Content Security Policy Level 2", December 2016,
<https://www.w3.org/TR/CSP2>.
[I-D.bradley-oauth-jwt-encoded-state]
Bradley, J., Lodderstedt, T., and H. Zandbelt, "Encoding
claims in the OAuth 2 state parameter using a JWT", Work
in Progress, Internet-Draft, draft-bradley-oauth-jwt-
encoded-state-09, 4 November 2018, <http://www.ietf.org/
internet-drafts/draft-bradley-oauth-jwt-encoded-state-
09.txt>.
[I-D.ietf-oauth-access-token-jwt]
Bertocci, V., "JSON Web Token (JWT) Profile for OAuth 2.0
Access Tokens", Work in Progress, Internet-Draft, draft-
ietf-oauth-access-token-jwt-07, 27 April 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-oauth-
access-token-jwt-07.txt>.
[I-D.ietf-oauth-browser-based-apps]
Parecki, A. and D. Waite, "OAuth 2.0 for Browser-Based
Apps", Work in Progress, Internet-Draft, draft-ietf-oauth-
browser-based-apps-06, 5 April 2020, <http://www.ietf.org/
internet-drafts/draft-ietf-oauth-browser-based-apps-
06.txt>.
[I-D.ietf-oauth-dpop]
Fett, D., Campbell, B., Bradley, J., Lodderstedt, T.,
Jones, M., and D. Waite, "OAuth 2.0 Demonstration of
Proof-of-Possession at the Application Layer (DPoP)", Work
in Progress, Internet-Draft, draft-ietf-oauth-dpop-01, 1
May 2020, <http://www.ietf.org/internet-drafts/draft-ietf-
oauth-dpop-01.txt>.
[I-D.ietf-oauth-par]
Lodderstedt, T., Campbell, B., Sakimura, N., Tonge, D.,
and F. Skokan, "OAuth 2.0 Pushed Authorization Requests",
Work in Progress, Internet-Draft, draft-ietf-oauth-par-01,
18 February 2020, <http://www.ietf.org/internet-drafts/
draft-ietf-oauth-par-01.txt>.
Hardt, et al. Expires 6 January 2021 [Page 76]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
[I-D.ietf-oauth-rar]
Lodderstedt, T., Richer, J., and B. Campbell, "OAuth 2.0
Rich Authorization Requests", Work in Progress, Internet-
Draft, draft-ietf-oauth-rar-01, 19 February 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-oauth-rar-
01.txt>.
[I-D.ietf-oauth-token-binding]
Jones, M., Campbell, B., Bradley, J., and W. Denniss,
"OAuth 2.0 Token Binding", Work in Progress, Internet-
Draft, draft-ietf-oauth-token-binding-08, 19 October 2018,
<http://www.ietf.org/internet-drafts/draft-ietf-oauth-
token-binding-08.txt>.
[NIST800-63]
Burr, W., Dodson, D., Newton, E., Perlner, R., Polk, T.,
Gupta, S., and E. Nabbus, "NIST Special Publication
800-63-1, INFORMATION SECURITY", December 2011,
<http://csrc.nist.gov/publications/>.
[OMAP] Huff, J., Schlacht, D., Nadalin, A., Simmons, J.,
Rosenberg, P., Madsen, P., Ace, T., Rickelton-Abdi, C.,
and B. Boyer, "Online Multimedia Authorization Protocol:
An Industry Standard for Authorized Access to Internet
Multimedia Resources", April 2012,
<https://www.oatc.us/Standards/Download-Standards>.
[OpenID] Sakimora, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0", November 2014,
<https://openiD.net/specs/openiD-connect-core-1_0.html>.
[OpenID.Messages]
Sakimura, N., Bradley, J., Jones, M., de Medeiros, B.,
Mortimore, C., and E. Jay, "OpenID Connect Messages 1.0",
June 2012, <http://openid.net/specs/openid-connect-
messages-1_0.html>.
[owasp_redir]
"OWASP Cheat Sheet Series - Unvalidated Redirects and
Forwards", 2020,
<https://cheatsheetseries.owasp.org/cheatsheets/
Unvalidated_Redirects_and_Forwards_Cheat_Sheet.html>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/info/rfc6265>.
Hardt, et al. Expires 6 January 2021 [Page 77]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
[RFC6819] Lodderstedt, T., Ed., McGloin, M., and P. Hunt, "OAuth 2.0
Threat Model and Security Considerations", RFC 6819,
DOI 10.17487/RFC6819, January 2013,
<https://www.rfc-editor.org/info/rfc6819>.
[RFC7009] Lodderstedt, T., Ed., Dronia, S., and M. Scurtescu, "OAuth
2.0 Token Revocation", RFC 7009, DOI 10.17487/RFC7009,
August 2013, <https://www.rfc-editor.org/info/rfc7009>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Authentication", RFC 7235,
DOI 10.17487/RFC7235, June 2014,
<https://www.rfc-editor.org/info/rfc7235>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
[RFC7591] Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and
P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
RFC 7591, DOI 10.17487/RFC7591, July 2015,
<https://www.rfc-editor.org/info/rfc7591>.
[RFC7592] Richer, J., Ed., Jones, M., Bradley, J., and M. Machulak,
"OAuth 2.0 Dynamic Client Registration Management
Protocol", RFC 7592, DOI 10.17487/RFC7592, July 2015,
<https://www.rfc-editor.org/info/rfc7592>.
[RFC7636] Sakimura, N., Ed., Bradley, J., and N. Agarwal, "Proof Key
for Code Exchange by OAuth Public Clients", RFC 7636,
DOI 10.17487/RFC7636, September 2015,
<https://www.rfc-editor.org/info/rfc7636>.
[RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection",
RFC 7662, DOI 10.17487/RFC7662, October 2015,
<https://www.rfc-editor.org/info/rfc7662>.
[RFC8414] Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
Authorization Server Metadata", RFC 8414,
DOI 10.17487/RFC8414, June 2018,
<https://www.rfc-editor.org/info/rfc8414>.
Hardt, et al. Expires 6 January 2021 [Page 78]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
[RFC8628] Denniss, W., Bradley, J., Jones, M., and H. Tschofenig,
"OAuth 2.0 Device Authorization Grant", RFC 8628,
DOI 10.17487/RFC8628, August 2019,
<https://www.rfc-editor.org/info/rfc8628>.
[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/info/rfc8705>.
[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/info/rfc8707>.
Appendix A. Augmented Backus-Naur Form (ABNF) Syntax
This section provides Augmented Backus-Naur Form (ABNF) syntax
descriptions for the elements defined in this specification using the
notation of [RFC5234]. The ABNF below is defined in terms of Unicode
code points [W3C.REC-xml-20081126]; these characters are typically
encoded in UTF-8. Elements are presented in the order first defined.
Some of the definitions that follow use the "URI-reference"
definition from [RFC3986].
Some of the definitions that follow use these common definitions:
VSCHAR = %x20-7E
NQCHAR = %x21 / %x23-5B / %x5D-7E
NQSCHAR = %x20-21 / %x23-5B / %x5D-7E
UNICODECHARNOCRLF = %x09 /%x20-7E / %x80-D7FF /
%xE000-FFFD / %x10000-10FFFF
(The UNICODECHARNOCRLF definition is based upon the Char definition
in Section 2.2 of [W3C.REC-xml-20081126], but omitting the Carriage
Return and Linefeed characters.)
A.1. "client_id" Syntax
The "client_id" element is defined in Section 2.3.1:
client-id = *VSCHAR
A.2. "client_secret" Syntax
The "client_secret" element is defined in Section 2.3.1:
Hardt, et al. Expires 6 January 2021 [Page 79]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
client-secret = *VSCHAR
A.3. "response_type" Syntax
The "response_type" element is defined in Section 3.1.1 and
Section 8.4:
response-type = response-name *( SP response-name )
response-name = 1*response-char
response-char = "_" / DIGIT / ALPHA
A.4. "scope" Syntax
The "scope" element is defined in Section 3.3:
scope = scope-token *( SP scope-token )
scope-token = 1*NQCHAR
A.5. "state" Syntax
The "state" element is defined in Section 4.1.1, Section 4.1.2, and
Section 4.1.2.1:
state = 1*VSCHAR
A.6. "redirect_uri" Syntax
The "redirect_uri" element is defined in Section 4.1.1, and
Section 4.1.3:
redirect-uri = URI-reference
A.7. "error" Syntax
The "error" element is defined in Sections Section 4.1.2.1,
Section 5.2, 7.2, and 8.5:
error = 1*NQSCHAR
A.8. "error_description" Syntax
The "error_description" element is defined in Sections
Section 4.1.2.1, Section 5.2, and Section 7.3:
error-description = 1*NQSCHAR
Hardt, et al. Expires 6 January 2021 [Page 80]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
A.9. "error_uri" Syntax
The "error_uri" element is defined in Sections Section 4.1.2.1,
Section 5.2, and 7.2:
error-uri = URI-reference
A.10. "grant_type" Syntax
The "grant_type" element is defined in Sections Section 4.1.3,
Section 4.2.3, Section 4.2.2, Section 4.3, and Section 6:
grant-type = grant-name / URI-reference
grant-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
A.11. "code" Syntax
The "code" element is defined in Section 4.1.3:
code = 1*VSCHAR
A.12. "access_token" Syntax
The "access_token" element is defined in Section 4.2.3 and
Section 5.1:
access-token = 1*VSCHAR
A.13. "token_type" Syntax
The "token_type" element is defined in Section 5.1, and Section 8.1:
token-type = type-name / URI-reference
type-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
A.14. "expires_in" Syntax
The "expires_in" element is defined in Section 5.1:
expires-in = 1*DIGIT
A.15. "refresh_token" Syntax
The "refresh_token" element is defined in Section 5.1 and Section 6:
refresh-token = 1*VSCHAR
Hardt, et al. Expires 6 January 2021 [Page 81]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
A.16. Endpoint Parameter Syntax
The syntax for new endpoint parameters is defined in Section 8.2:
param-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA
A.17. "code_verifier" Syntax
ABNF for "code_verifier" is as follows.
code-verifier = 43*128unreserved
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
ALPHA = %x41-5A / %x61-7A
DIGIT = %x30-39
A.18. "code_challenge" Syntax
ABNF for "code_challenge" is as follows.
code-challenge = 43*128unreserved
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
ALPHA = %x41-5A / %x61-7A
DIGIT = %x30-39
Appendix B. Use of application/x-www-form-urlencoded Media Type
At the time of publication of this specification, the "application/x-
www-form-urlencoded" media type was defined in Section 17.13.4 of
[W3C.REC-html401-19991224] but not registered in the IANA MIME Media
Types registry (http://www.iana.org/assignments/media-types
(http://www.iana.org/assignments/media-types)). Furthermore, that
definition is incomplete, as it does not consider non-US-ASCII
characters.
To address this shortcoming when generating payloads using this media
type, names and values MUST be encoded using the UTF-8 character
encoding scheme [RFC3629] first; the resulting octet sequence then
needs to be further encoded using the escaping rules defined in
[W3C.REC-html401-19991224].
When parsing data from a payload using this media type, the names and
values resulting from reversing the name/value encoding consequently
need to be treated as octet sequences, to be decoded using the UTF-8
character encoding scheme.
Hardt, et al. Expires 6 January 2021 [Page 82]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
For example, the value consisting of the six Unicode code points (1)
U+0020 (SPACE), (2) U+0025 (PERCENT SIGN), (3) U+0026 (AMPERSAND),
(4) U+002B (PLUS SIGN), (5) U+00A3 (POUND SIGN), and (6) U+20AC (EURO
SIGN) would be encoded into the octet sequence below (using
hexadecimal notation):
20 25 26 2B C2 A3 E2 82 AC
and then represented in the payload as:
+%25%26%2B%C2%A3%E2%82%AC
Appendix C. Extensions
Below is a list of well-established extensions at the time of
publication:
* [RFC8628]: OAuth 2.0 Device Authorization Grant
- The Device Authorization Grant (formerly known as the Device
Flow) is an extension that enables devices with no browser or
limited input capability to obtain an access token. This is
commonly used by smart TV apps, or devices like hardware video
encoders that can stream video to a streaming video service.
* [RFC8414]: Authorization Server Metadata
- Authorization Server Metadata (also known as OAuth Discovery)
defines an endpoint clients can use to look up the information
needed to interact with a particular OAuth server, such as the
location of the authorization and token endpoints and the
supported grant types.
* [RFC8707]: Resource Indicators
- Provides a way for the client to explicitly signal to the
authorization server where it intends to use the access token
it is requesting.
* [RFC7591]: Dynamic Client Registration
- Dynamic Client Registration provides a mechanism for
programmatically registering clients with an authorization
server.
* [RFC7592]: Dynamic Client Management
Hardt, et al. Expires 6 January 2021 [Page 83]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
- Dynamic Client Management provides a mechanism for updating
dynamically registered client information.
* [I-D.ietf-oauth-access-token-jwt]: JSON Web Token (JWT) Profile
for OAuth 2.0 Access Tokens
- This specification defines a profile for issuing OAuth access
tokens in JSON web token (JWT) format.
* [RFC8705]: Mutual TLS
- Mutual TLS describes a mechanism of binding access tokens and
refresh tokens to the clients they were issued to, as well as a
client authentication mechanism, via TLS certificate
authentication.
* [RFC7662]: Token Introspection
- The Token Introspection extension defines a mechanism for
resource servers to obtain information about access tokens.
* [RFC7009]: Token Revocation
- The Token Revocation extension defines a mechanism for clients
to indicate to the authorization server that an access token is
no longer needed.
* [I-D.ietf-oauth-par]: Pushed Authorization Requests
- The Pushed Authorization Requsts extension describes a
technique of initiating an OAuth flow from the back channel,
providing better security and more flexibility for building
complex authorization requests.
* [I-D.ietf-oauth-rar]: Rich Authorization Requests
- Rich Authorization Requests specifies a new parameter
"authorization_details" that is used to carry fine-grained
authorization data in the OAuth authorization request.
Appendix D. Acknowledgements
TBD
Authors' Addresses
Hardt, et al. Expires 6 January 2021 [Page 84]
Internet-Draft The OAuth 2.1 Authorization Framework July 2020
Dick Hardt
SignIn.Org
Email: dick.hardt@gmail.com
Aaron Parecki
Okta
Email: aaron@parecki.com
URI: https://aaronparecki.com
Torsten Lodderstedt
yes.com
Email: torsten@lodderstedt.net
Hardt, et al. Expires 6 January 2021 [Page 85]
