Internet DRAFT - draft-parecki-oauth-identity-assertion-authz-grant
draft-parecki-oauth-identity-assertion-authz-grant
Web Authorization Protocol A. Parecki
Internet-Draft K. McGuinness
Intended status: Standards Track Okta
Expires: 3 September 2024 2 March 2024
Identity Assertion Authorization Grant
draft-parecki-oauth-identity-assertion-authz-grant-00
Abstract
This specification provides a mechanism for an application to use an
identity assertion to obtain an access token for a third-party API
using Token Exchange [RFC8693] and JWT Profile for OAuth 2.0
Authorization Grants [RFC7523].
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://aaronpk.github.io/draft-parecki-oauth-identity-assertion-
authz-grant/draft-parecki-oauth-identity-assertion-authz-grant.html.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-parecki-oauth-identity-
assertion-authz-grant/.
Discussion of this document takes place on the Web Authorization
Protocol Working Group mailing list (mailto:oauth@ietf.org), which is
archived at https://mailarchive.ietf.org/arch/browse/oauth/.
Subscribe at https://www.ietf.org/mailman/listinfo/oauth/.
Source for this draft and an issue tracker can be found at
https://github.com/aaronpk/draft-parecki-oauth-identity-assertion-
authz-grant.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
2.1. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. User Authentication . . . . . . . . . . . . . . . . . . . . . 6
5. Token Exchange . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Processing Rules . . . . . . . . . . . . . . . . . . . . 7
5.2. Response . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2.1. Error Response . . . . . . . . . . . . . . . . . . . 8
5.3. Identity Assertion Authorization Grant JWT . . . . . . . 9
6. Access Token Request . . . . . . . . . . . . . . . . . . . . 10
6.1. Processing Rules . . . . . . . . . . . . . . . . . . . . 10
6.2. Response . . . . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7.1. Client Authentication . . . . . . . . . . . . . . . . . . 11
7.2. Step-Up Authentication . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8.1. Media Types . . . . . . . . . . . . . . . . . . . . . . . 12
8.2. OAuth URI Registration . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Use Cases . . . . . . . . . . . . . . . . . . . . . 14
A.1. Enterprise Deployment . . . . . . . . . . . . . . . . . . 14
A.1.1. Preconditions . . . . . . . . . . . . . . . . . . . . 14
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A.2. Email and Calendaring Applications . . . . . . . . . . . 15
A.2.1. Preconditions . . . . . . . . . . . . . . . . . . . . 15
Appendix B. Relationship to RFC7522 . . . . . . . . . . . . . . 16
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
The draft specification Identity Chaining Across Trust Domains
[I-D.ietf-oauth-identity-chaining] defines how to request a JWT
authorization grant from an Authorization Server and exchange it for
an Access Token at another Authorization Server in a different trust
domain. The specification is an application of a combination of
OAuth 2.0 Token Exchange [RFC8693] and JSON Web Token (JWT) Profile
for OAuth 2.0 Client Authentication and Authorization Grants
[RFC7523]. The draft supports multiple different use cases by
leaving many details of the token exchange request and JWT
authorization grant unspecified. This specification defines the
additional details necessary to support interoperable implementations
when using identity tokens as the input to the token exchange
request.
2. Conventions and Definitions
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.
2.1. Roles
Client Application that wants to obtain an OAuth 2.0 access token on
behalf of a signed-in user to an external/3rd party application's
API (Resource Server below). In
[I-D.ietf-oauth-identity-chaining], this is the Client in trust
domain A.
Resource Application Application that provides an OAuth 2.0
Protected Resource. In [I-D.ietf-oauth-identity-chaining], this
is the Protected Resource in trust domain B.
Authorization Server (IdP) The Identity Provider that is trusted by
a set of applications in an organization's app ecosystem. In
[I-D.ietf-oauth-identity-chaining], this is the Authorization
Server in trust domain A, which is also trusted by the
Authorization Server of the Protected Resource in trust domain B.
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3. Overview
The example flow is for an enterprise acme
+===========+====================+=========================+=============+
|Role |App URL |Tenant URL |Description |
+===========+====================+=========================+=============+
|Client |https://wiki.example|https://acme.wiki.example|SaaS Wiki app|
| | | |that embeds |
| | | |content from |
| | | |one or more |
| | | |resource |
| | | |applications |
+-----------+--------------------+-------------------------+-------------+
|Resource |https://chat.example|https://acme.chat.example|Chat and |
|Application| | |communication|
| | | |app |
+-----------+--------------------+-------------------------+-------------+
|Identity |https://idp.example |https://acme.idp.example |Identity |
|Provider | | |Provider |
+-----------+--------------------+-------------------------+-------------+
Table 1
Sequence Diagram
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+---------+ +--------------+ +---------------+ +--------------+
| | | | | Resource | | Resource |
| | | IdP | | Application | | Application |
| Client | | Authorization| | Authorization | | Resource |
| | | Server | | Server | | Server |
+----+----+ +-------+------+ +-------+-------+ +------+-------+
| | | |
| | | |
| --------------> | | |
| 1 User SSO | | |
| | | |
| ID Token | | |
| <- - - - - - - - | | |
| | | |
| | | |
| | | |
| 2 Token Exchange | | |
| ----------------> | | |
| | | |
| ID-JAG | | |
| <- - - - - - - - | | |
| | | |
| | | |
| | | |
| 3 Present ID-JAG | | |
| ------------------+----------------> | |
| | | |
| Access Token | | |
| <- - - - - - - - - - - - - - - - - - | |
| | | |
| | | |
| | | |
| 4 Resource Request with Access Token| |
| -----------------------------------------------------> |
| | | |
| | | |
| | | |
1. User logs in to the Client, the Client obtains the Identity
Assertion (e.g. SAML Assertion or OpenID Connect ID Token)
2. Client uses the Identity Assertion to request an Identity
Assertion Authorization Grant for the Resource Application from
the IdP
3. Client exchanges the Identity Assertion Authorization Grant JWT
for an Access Token at the Resource Application's token endpoint
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4. Client makes an API request with the Access Token
4. User Authentication
The Client initiates an authentication request with the IdP using
OpenID Connect or SAML.
The following is an example using OpenID Connect
302 Redirect
Location: https://acme.idp.example/authorize?response_type=code&scope=openid&client_id=...
The user authenticates with the IdP, and is redirected back to the
Client with an authorization code, which it can then exchange for an
ID Token.
Note: The Enterprise IdP may enforce security controls such as multi-
factor authentication before granting the user access to the Client.
POST /token HTTP/1.1
Host: acme.idp.example
Content-Type: application/x-www-form-urlencoded
grant_type=authorization_code
&code=.....
HTTP/1.1 200 Ok
Content-Type: application/json
{
"id_token": "eyJraWQiOiJzMTZ0cVNtODhwREo4VGZCXzdrSEtQ...",
"token_type": "Bearer",
"access_token": "7SliwCQP1brGdjBtsaMnXo",
"scope": "openid"
}
5. Token Exchange
The Client makes a Token Exchange [RFC8693] request to the IdP's
Token Endpoint with the following parameters:
* requested_token_type=urn:ietf:params:oauth:token-type:id-jag
* resource - The token endpoint of the Resource Application.
* scope - The space-separated list of scopes at the Resource
Application to include in the token
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* subject_token - The identity assertion (SAML Assertion or OpenID
Connect ID Token) for the target end-user
* subject_token_type - For SAML2 Assertion:
urn:ietf:params:oauth:token-type:saml2, or OpenID Connect ID
Token: urn:ietf:params:oauth:token-type:id_token
* Client authentication (e.g. client_id and client_secret, or the
more secure private_key_jwt method using client_assertion and
client_assertion_type)
The example below uses an ID Token as the Identity Assertion, and
uses private_key_jwt as the client authentication method, (tokens
truncated for brevity):
POST /oauth2/token HTTP/1.1
Host: acme.idp.example
Content-Type: application/x-www-form-urlencoded
grant_type=urn:ietf:params:oauth:grant-type:token-exchange
&requested_token_type=urn:ietf:params:oauth:token-type:id-jag
&resource=https://acme.chat.example/oauth2/token
&scope=chat.read+chat.history
&subject_token=eyJraWQiOiJzMTZ0cVNtODhwREo4VGZCXzdrSEtQ...
&subject_token_type=urn:ietf:params:oauth:token-type:id_token
&client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer
&client_assertion=eyJhbGciOiJSUzI1NiIsImtpZCI6IjIyIn0...
5.1. Processing Rules
The IdP MUST validate the subject token, and MUST validate that the
audience of the Subject Token (e.g. the aud claim of the ID Token)
matches the client_id of the client authentication of the request.
The IdP evaluates administrator-defined policy for the token exchange
request and determines if the client should be granted access to act
on behalf of the subject for the target audience and scopes.
The IdP may also introspect the authentication context described in
the SSO assertion to determine if step-up authentication is required.
5.2. Response
If access is granted, the IdP creates a signed Identity Assertion
Authorization Grant JWT and returns it in the token exchange response
defined in Section 2.2 of [RFC8693]:
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HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache
{
"issued_token_type": "urn:ietf:params:oauth:token-type:id-jag",
"access_token": "eyJhbGciOiJIUzI1NiIsI...",
"token_type": "N_A",
"scope": "chat.read chat.history",
"expires_in": 300
}
* issued_token_type - urn:ietf:params:oauth:token-type:id-jag
* access_token - The Identity Assertion Authorization Grant JWT.
(Token Exchange requires the access_token response parameter for
historical reasons, even though this is not an OAuth access
token.)
* token_type - N_A (As defined by Token Exchange.)
* scope - The list of scopes granted by the IdP. This may be fewer
scopes than the application requested based on various policies in
the IdP.
* expires_in - The lifetime in seconds of the authorization grant.
5.2.1. Error Response
On an error condition, the IdP returns an OAuth 2.0 Token Error
response as defined in Section 5.2 of [RFC6749], e.g:
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
{
"error": "invalid_grant",
"error_description": "Audience validation failed"
}
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5.3. Identity Assertion Authorization Grant JWT
The Identity Assertion Authorization Grant JWT is issued and signed
by the IdP, and describes the intended audience of the authorization
grant as well as the client to which it was issued and the subject
identifier of the original identity assertion, using the following
claims:
* iss - The IdP issuer URL
* sub - The User ID at the IdP
* aud - Token endpoint of the Resource Application's authorization
server
* client_id - Client ID as registered with the Resource
Application's authorization server.
* scopes - Array of scopes at the Resource Application granted to
the Client
* jti - Unique ID of this JWT
* exp, iat - as defined by JWT
The typ of the JWT indicated in the JWT header MUST be oauth-id-
jag+jwt.
An example JWT shown with expanded header and payload claims is
below:
{
"typ": "oauth-id-jag+jwt"
}
.
{
"jti": "9e43f81b64a33f20116179",
"iss": "https://acme.idp.example",
"sub": "U019488227",
"aud": "https://acme.chat.example/oauth2/token",
"client_id": "f53f191f9311af35",
"exp": 1311281970,
"iat": 1311280970,
"scopes" : [ "chat.read" , "chat.history" ]
}
.
signature
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Implementation notes:
* If the IdP is multi-tenant and uses the same issuer for all
tenants, the Resource Application will already have IdP-specific
logic to determine the tenant from OIDC/SAML (e.g. the hd claim in
Google) and will need to use that if the IdP also has only one
client registration for the Resource Application.
* sub should be an opaque ID, as iss+sub is unique. The IdP might
want to also include the user's email here, which it should do as
a new email claim. This would let the app dedupe existing users
who may have an account with an email address but have not done
SSO yet.
6. Access Token Request
The Client makes an access token request to the Resource
Application's token endpoint using the previously obtained Identity
Assertion Authorization Grant as a JWT Assertion [RFC7523].
* grant_type=urn:ietf:params:oauth:grant-type:jwt-bearer
* assertion - The Identity Assertion Authorization Grant JWT
obtained in the previous token exchange step
* Client Authentication - the Client authenticates with its
credentials as registered with the Resource Application's
authorization server
For example:
POST /oauth2/token HTTP/1.1
Host: acme.chat.example
Authorization: Basic yZS1yYW5kb20tc2VjcmV0v3JOkF0XG5Qx2
grant_type=urn:ietf:params:oauth:grant-type:jwt-bearer
assertion=eyJhbGciOiJIUzI1NiIsI...
6.1. Processing Rules
All of Section 5.2 of [RFC7521] applies, in addition to the following
processing rules:
* Validate the JWT typ is oauth-id-jag+jwt (per [RFC8725])
* The aud claim MUST identify the token endpoint of the Resource
Application as the intended audience of the JWT.
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6.2. Response
The Resource Application token endpoint responds with an OAuth 2.0
Token Response, e.g.:
HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Cache-Control: no-store
Pragma: no-cache
{
"token_type": "Bearer",
"access_token": "2YotnFZFEjr1zCsicMWpAA",
"expires_in": 86400,
"refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
}
7. Security Considerations
7.1. Client Authentication
This specification SHOULD only be supported for confidential clients.
Public clients SHOULD redirect the user with an OAuth 2.0
Authorization Request.
7.2. Step-Up Authentication
In the initial token exchange request, the IdP may require step-up
authentication for the subject if the authentication context in the
subject's assertion does not meet policy requirements. An
insufficient_user_authentication OAuth error response may be returned
to convey the authentication requirements back to the client similar
to OAuth 2.0 Step-up Authentication Challenge Protocol [RFC9470].
HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store
{
"error": "insufficient_user_authentication",
"error_description": "Subject doesn't meet authentication requirements",
"max_age": 5
}
The Client would need to redirect the user back to the IdP to obtain
a new assertion that meets the requirements and retry the token
exchange.
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TBD: It may make more sense to request the Identity Assertion
Authorization Grant as an additional response_type on the
authorization request if using OIDC for SSO when performing a step-up
to skip the need for additional token exchange round-trip.
8. IANA Considerations
8.1. Media Types
This section registers oauth-id-jag+jwt, a new media type [RFC2046]
in the "Media Types" registry [IANA.MediaTypes] in the manner
described in [RFC6838]. It can be used to indicate that the content
is a Identity Assertion Authorization Grant JWT.
8.2. OAuth URI Registration
This section registers urn:ietf:params:oauth:token-type:id-jag in the
"OAuth URI" subregistry of the "OAuth Parameters" registry
[IANA.oauth-parameters].
* URN: urn:ietf:params:oauth:token-type:id-jag
* Common Name: Token type URI for a Identity Assertion JWT
Authorization Grant
* Change Controller: IESG
* Specification Document: This document
9. References
9.1. Normative References
[I-D.ietf-oauth-identity-chaining]
Schwenkschuster, A., Kasselman, P., Burgin, K., Jenkins,
M. J., and B. Campbell, "OAuth Identity and Authorization
Chaining Across Domains", Work in Progress, Internet-
Draft, draft-ietf-oauth-identity-chaining-01, 19 February
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
oauth-identity-chaining-01>.
[IANA.MediaTypes]
"*** BROKEN REFERENCE ***".
[IANA.oauth-parameters]
IANA, "OAuth Parameters",
<http://www.iana.org/assignments/oauth-parameters>.
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[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/rfc/rfc2046>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/rfc/rfc6749>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/rfc/rfc6838>.
[RFC7521] Campbell, B., Mortimore, C., Jones, M., and Y. Goland,
"Assertion Framework for OAuth 2.0 Client Authentication
and Authorization Grants", RFC 7521, DOI 10.17487/RFC7521,
May 2015, <https://www.rfc-editor.org/rfc/rfc7521>.
[RFC7523] Jones, M., Campbell, B., and C. Mortimore, "JSON Web Token
(JWT) Profile for OAuth 2.0 Client Authentication and
Authorization Grants", RFC 7523, DOI 10.17487/RFC7523, May
2015, <https://www.rfc-editor.org/rfc/rfc7523>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8693] Jones, M., Nadalin, A., Campbell, B., Ed., Bradley, J.,
and C. Mortimore, "OAuth 2.0 Token Exchange", RFC 8693,
DOI 10.17487/RFC8693, January 2020,
<https://www.rfc-editor.org/rfc/rfc8693>.
[RFC8725] Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
Current Practices", BCP 225, RFC 8725,
DOI 10.17487/RFC8725, February 2020,
<https://www.rfc-editor.org/rfc/rfc8725>.
9.2. Informative References
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[RFC7522] Campbell, B., Mortimore, C., and M. Jones, "Security
Assertion Markup Language (SAML) 2.0 Profile for OAuth 2.0
Client Authentication and Authorization Grants", RFC 7522,
DOI 10.17487/RFC7522, May 2015,
<https://www.rfc-editor.org/rfc/rfc7522>.
[RFC9470] Bertocci, V. and B. Campbell, "OAuth 2.0 Step Up
Authentication Challenge Protocol", RFC 9470,
DOI 10.17487/RFC9470, September 2023,
<https://www.rfc-editor.org/rfc/rfc9470>.
Appendix A. Use Cases
A.1. Enterprise Deployment
Enterprises often have hundreds of SaaS applications. SaaS
applications often have integrations to other SaaS applications that
are critical to the application experience and jobs to be done. When
a SaaS app needs to request an access token on behalf of a user to a
3rd party SaaS integration's API, the end-user typically needs to
complete an interactive delegated OAuth 2.0 flow, as the SaaS
application is not in the same security or policy domain as the 3rd
party SaaS integration.
It is industry best practice for an enterprise to connect their
ecosystem of SaaS applications to their Identity Provider (IdP) to
centralize identity and access management capabilites for the
organization. End-users get a better experience (SSO) and
administrators get better security outcomes such multi-factor
authentication and zero-trust. SaaS applications today enable the
administrator to establish trust with an IdP for user authentication.
This specification can be used to extend the SSO relationship of
multiple SaaS applications to include API access between these
applications as well. This specification enables federation for
Authorization Servers across policy or administrative boundaries.
The same enterprise IdP that is trusted by applications for SSO can
be extended to broker access to APIs. This enables the enterprise to
centralize more access decisions across their SaaS ecosystem and
provides better end-user experience for users that need to connect
multiple applications via OAuth 2.0.
A.1.1. Preconditions
* The Client has a registered OAuth 2.0 Client with the IdP
Authorization Server
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* The Client has a registered OAuth 2.0 Client with the Resource
Application
* Enterprise has established a trust relationship between their IdP
and the Client for SSO and Identity Assertion Authorization Grant
* Enterprise has established a trust relationship between their IdP
and the Resource Application for SSO and Identity Assertion
Authorization Grant
* Enterprise has granted the Client permission to act on behalf of
users for the Resource Application with a set of scopes
A.2. Email and Calendaring Applications
Email clients can be used with arbitrary email servers, and cannot
require pre-established relationships between each email client and
each email server. When an email client uses OAuth to obtain an
access token to an email server, this provides the security benefit
of being able to use strong multi-factor authentication methods
provided by the email server's authorization server, but does require
that the user go through a web-based flow to log in to the email
client. However, this web-based flow is often seen as distruptive to
the user experience when initiated from a desktop or mobile native
application, and so is often attempted to be minimized as much as
possible.
When the email client needs access to a separate API, such as a
third-party calendaring application, traditionally this would require
that the email client go through another web-based OAuth redirect
flow to obtain authorization and ultimately an access token.
To streamline the user experience, this specification can be used to
enable the email client to use the identity assertion to obtain an
access token for the third-party calendaring application without any
user interaction.
A.2.1. Preconditions
* The Client does not have a pre-registered OAuth 2.0 client at the
IdP Authorization Server or the Resource Application
* The Client has obtained an Identity Assertion (e.g. ID Token)
from the IdP Authorization Server
* The Resource Application is configured to allow the Identity
Assertion Authorization Grant from unregistered clients
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Appendix B. Relationship to RFC7522
"SAML 2.0 Profile for OAuth 2.0 Client Authentication and
Authorization Grants" [RFC7522] describes a mechanism for using a
SAML assertion as an authorization grant to obtain an access token.
Directly exchanging a SAML assertion for an access token is limited
in the ways this can be securely deployed.
This specification adds an intermediate step of exchanging a SAML
assertion for the intermediate Identity Assertion Authorization
Grant, which is then later exchanged for an access token. By adding
this intermediate step, this provides the security benefit of being
able to indicate which API the access token is being requested,
enabling the authorization server to enforce policies before issuing
the authorization grant. Without this step, policies must be
enforced at each resource application's authorization server, which
doesn't scale well and is impossible in some deployments.
Acknowledgments
The authors would like to thank the following people for their
contributions and reviews of this specification: Brian Campbell.
Authors' Addresses
Aaron Parecki
Okta
Email: aaron@parecki.com
Karl McGuinness
Okta
Email: public@karlmcguinness.com
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