OAuth 2.0 Pushed Authorization Requests
RFC 9126

Document Type RFC - Proposed Standard (September 2021; Errata)
Authors Torsten Lodderstedt  , Brian Campbell  , Nat Sakimura  , Dave Tonge  , Filip Skokan 
Last updated 2021-10-16
Replaces draft-lodderstedt-oauth-par
Stream Internet Engineering Task Force (IETF)
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Internet Engineering Task Force (IETF)                    T. Lodderstedt
Request for Comments: 9126                                       yes.com
Category: Standards Track                                    B. Campbell
ISSN: 2070-1721                                            Ping Identity
                                                             N. Sakimura
                                                          NAT.Consulting
                                                                D. Tonge
                                           Moneyhub Financial Technology
                                                               F. Skokan
                                                                   Auth0
                                                          September 2021

                OAuth 2.0 Pushed Authorization Requests

Abstract

   This document defines the pushed authorization request (PAR)
   endpoint, which allows clients to push the payload of an OAuth 2.0
   authorization request to the authorization server via a direct
   request and provides them with a request URI that is used as
   reference to the data in a subsequent call to the authorization
   endpoint.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9126.

Copyright Notice

   Copyright (c) 2021 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 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
     1.1.  Introductory Example
     1.2.  Conventions and Terminology
   2.  Pushed Authorization Request Endpoint
     2.1.  Request
     2.2.  Successful Response
     2.3.  Error Response
     2.4.  Management of Client Redirect URIs
   3.  The "request" Request Parameter
   4.  Authorization Request
   5.  Authorization Server Metadata
   6.  Client Metadata
   7.  Security Considerations
     7.1.  Request URI Guessing
     7.2.  Open Redirection
     7.3.  Request Object Replay
     7.4.  Client Policy Change
     7.5.  Request URI Swapping
   8.  Privacy Considerations
   9.  IANA Considerations
     9.1.  OAuth Authorization Server Metadata
     9.2.  OAuth Dynamic Client Registration Metadata
     9.3.  OAuth URI Registration
   10. References
     10.1.  Normative References
     10.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   This document defines the pushed authorization request (PAR)
   endpoint, which enables an OAuth [RFC6749] client to push the payload
   of an authorization request directly to the authorization server.  A
   request URI value is received in exchange; it is used as reference to
   the authorization request payload data in a subsequent call to the
   authorization endpoint via the user agent.

   In OAuth [RFC6749], authorization request parameters are typically
   sent as URI query parameters via redirection in the user agent.  This
   is simple but also yields challenges:

   *  There is no cryptographic integrity and authenticity protection.
      An attacker could, for example, modify the scope of access
      requested or swap the context of a payment transaction by changing
      scope values.  Although protocol facilities exist to enable
      clients or users to detect some such changes, preventing
      modifications early in the process is a more robust solution.

   *  There is no mechanism to ensure confidentiality of the request
      parameters.  Although HTTPS is required for the authorization
      endpoint, the request data passes through the user agent in the
      clear, and query string data can inadvertently leak to web server
      logs and to other sites via the referrer.  The impact of such
      leakage can be significant, if personally identifiable information
      or other regulated data is sent in the authorization request
      (which might well be the case in identity, open banking, and
      similar scenarios).

   *  Authorization request URLs can become quite large, especially in
      scenarios requiring fine-grained authorization data, which might
      cause errors in request processing.

   JWT-Secured Authorization Request (JAR) [RFC9101] provides solutions
   for the security challenges by allowing OAuth clients to wrap
   authorization request parameters in a Request Object, which is a
   signed and optionally encrypted JSON Web Token (JWT) [RFC7519].  In
   order to cope with the size restrictions, JAR introduces the
   "request_uri" parameter that allows clients to send a reference to a
   Request Object instead of the Request Object itself.

   This document complements JAR by providing an interoperable way to
   push the payload of an authorization request directly to the
   authorization server in exchange for a "request_uri" value usable at
   the authorization server in a subsequent authorization request.

   PAR fosters OAuth security by providing clients a simple means for a
   confidential and integrity-protected authorization request.  Clients
   requiring an even higher security level, especially cryptographically
   confirmed non-repudiation, are able to use JWT-based Request Objects
   as defined by [RFC9101] in conjunction with PAR.

   PAR allows the authorization server to authenticate the client before
   any user interaction happens.  The increased confidence in the
   identity of the client during the authorization process allows the
   authorization server to refuse illegitimate requests much earlier in
   the process, which can prevent attempts to spoof clients or otherwise
   tamper with or misuse an authorization request.

   Note that HTTP "POST" requests to the authorization endpoint via the
   user agent, as described in Section 3.1 of [RFC6749] and
   Section 3.1.2.1 of [OIDC], could also be used to cope with the
   request size limitations described above.  However, it's only
   optional per [RFC6749], and, even when supported, it is a viable
   option for conventional web applications but is prohibitively
   difficult to use with installed mobile applications.  As described in
   [RFC8252], those apps use platform-specific APIs to open the
   authorization request URI in the system browser.  When a mobile app
   launches a browser, however, the resultant initial request is
   constrained to use the "GET" method.  Using "POST" for the
   authorization request would require the app to first direct the
   browser to open a URI that the app controls via "GET" while somehow
   conveying the sizable authorization request payload and then having
   the resultant response contain the content and script to initiate a
   cross-site form "POST" towards the authorization server.  PAR is
   simpler to use and has additional security benefits, as described
   above.

1.1.  Introductory Example

   In conventional OAuth 2.0, a client typically initiates an
   authorization request by directing the user agent to make an HTTP
   request like the following to the authorization server's
   authorization endpoint (extra line breaks and indentation for display
   purposes only):

    GET /authorize?response_type=code
     &client_id=CLIENT1234&state=duk681S8n00GsJpe7n9boxdzen
     &redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb HTTP/1.1
    Host: as.example.com

   Such a request could instead be pushed directly to the authorization
   server by the client with a "POST" request to the PAR endpoint as
   illustrated in the following example (extra line breaks and spaces
   for display purposes only).  The client can authenticate (e.g., using
   JWT client assertion-based authentication as shown) because the
   request is made directly to the authorization server.

    POST /as/par HTTP/1.1
    Host: as.example.com
    Content-Type: application/x-www-form-urlencoded

    &response_type=code
    &client_id=CLIENT1234&state=duk681S8n00GsJpe7n9boxdzen
    &redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb
    &client_assertion_type=
     urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
    &client_assertion=eyJraWQiOiI0MiIsImFsZyI6IkVTMjU2In0.eyJpc3MiOiJDTE
     lFTlQxMjM0Iiwic3ViIjoiQ0xJRU5UMTIzNCIsImF1ZCI6Imh0dHBzOi8vc2VydmVyL
     mV4YW1wbGUuY29tIiwiZXhwIjoxNjI1ODY4ODc4fQ.Igw8QrpAWRNPDGoWGRmJumLBM
     wbLjeIYwqWUu-ywgvvufl_0sQJftNs3bzjIrP0BV9rRG-3eI1Ksh0kQ1CwvzA

   The authorization server responds with a request URI:

    HTTP/1.1 201 Created
    Cache-Control: no-cache, no-store
    Content-Type: application/json

    {
      "request_uri": "urn:example:bwc4JK-ESC0w8acc191e-Y1LTC2",
      "expires_in": 90
    }

   The client uses the request URI value to create the subsequent
   authorization request by directing the user agent to make an HTTP
   request to the authorization server's authorization endpoint like the
   following (extra line breaks and indentation for display purposes
   only):

    GET /authorize?client_id=CLIENT1234
     &request_uri=urn%3Aexample%3Abwc4JK-ESC0w8acc191e-Y1LTC2 HTTP/1.1
    Host: as.example.com

1.2.  Conventions and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This specification uses the terms "access token", "authorization
   server", "authorization endpoint", "authorization request", "token
   endpoint", and "client" defined by "The OAuth 2.0 Authorization
   Framework" [RFC6749].

2.  Pushed Authorization Request Endpoint

   The pushed authorization request endpoint is an HTTP API at the
   authorization server that accepts HTTP "POST" requests with
   parameters in the HTTP request message body using the "application/x-
   www-form-urlencoded" format.  This format has a character encoding of
   UTF-8, as described in Appendix B of [RFC6749].  The PAR endpoint URL
   MUST use the "https" scheme.

   Authorization servers supporting PAR SHOULD include the URL of their
   pushed authorization request endpoint in their authorization server
   metadata document [RFC8414] using the
   "pushed_authorization_request_endpoint" parameter as defined in
   Section 5.

   The endpoint accepts the authorization request parameters defined in
   [RFC6749] for the authorization endpoint as well as all applicable
   extensions defined for the authorization endpoint.  Some examples of
   such extensions include Proof Key for Code Exchange (PKCE) [RFC7636],
   Resource Indicators [RFC8707], and OpenID Connect (OIDC) [OIDC].  The
   endpoint MAY also support sending the set of authorization request
   parameters as a Request Object according to [RFC9101] and Section 3
   of this document.

   The rules for client authentication as defined in [RFC6749] for token
   endpoint requests, including the applicable authentication methods,
   apply for the PAR endpoint as well.  If applicable, the
   "token_endpoint_auth_method" client metadata parameter [RFC7591]
   indicates the registered authentication method for the client to use
   when making direct requests to the authorization server, including
   requests to the PAR endpoint.  Similarly, the
   "token_endpoint_auth_methods_supported" authorization server metadata
   [RFC8414] parameter lists client authentication methods supported by
   the authorization server when accepting direct requests from clients,
   including requests to the PAR endpoint.

   Due to historical reasons, there is potential ambiguity regarding the
   appropriate audience value to use when employing JWT client
   assertion-based authentication (defined in Section 2.2 of [RFC7523]
   with "private_key_jwt" or "client_secret_jwt" authentication method
   names per Section 9 of [OIDC]).  To address that ambiguity, the
   issuer identifier URL of the authorization server according to
   [RFC8414] SHOULD be used as the value of the audience.  In order to
   facilitate interoperability, the authorization server MUST accept its
   issuer identifier, token endpoint URL, or pushed authorization
   request endpoint URL as values that identify it as an intended
   audience.

2.1.  Request

   A client sends the parameters that comprise an authorization request
   directly to the PAR endpoint.  A typical parameter set might include:
   "client_id", "response_type", "redirect_uri", "scope", "state",
   "code_challenge", and "code_challenge_method" as shown in the example
   below.  However, the pushed authorization request can be composed of
   any of the parameters applicable for use at the authorization
   endpoint, including those defined in [RFC6749] as well as all
   applicable extensions.  The "request_uri" authorization request
   parameter is one exception, and it MUST NOT be provided.

   The request also includes, as appropriate for the given client, any
   additional parameters necessary for client authentication (e.g.,
   "client_secret" or "client_assertion" and "client_assertion_type").
   Such parameters are defined and registered for use at the token
   endpoint but are applicable only for client authentication.  When
   present in a pushed authorization request, they are relied upon only
   for client authentication and are not germane to the authorization
   request itself.  Any token endpoint parameters that are not related
   to client authentication have no defined meaning for a pushed
   authorization request.  The "client_id" parameter is defined with the
   same semantics for both authorization requests and requests to the
   token endpoint; as a required authorization request parameter, it is
   similarly required in a pushed authorization request.

   The client constructs the message body of an HTTP "POST" request with
   parameters formatted with "x-www-form-urlencoded" using a character
   encoding of UTF-8, as described in Appendix B of [RFC6749].  If
   applicable, the client also adds its authentication credentials to
   the request header or the request body using the same rules as for
   token endpoint requests.

   This is illustrated by the following example (extra line breaks in
   the message body for display purposes only):

    POST /as/par HTTP/1.1
    Host: as.example.com
    Content-Type: application/x-www-form-urlencoded

    response_type=code&state=af0ifjsldkj&client_id=s6BhdRkqt3
    &redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb
    &code_challenge=K2-ltc83acc4h0c9w6ESC_rEMTJ3bww-uCHaoeK1t8U
    &code_challenge_method=S256&scope=account-information
    &client_assertion_type=
     urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
    &client_assertion=eyJraWQiOiJrMmJkYyIsImFsZyI6IlJTMjU2In0.eyJpc3Mi
     OiJzNkJoZFJrcXQzIiwic3ViIjoiczZCaGRSa3F0MyIsImF1ZCI6Imh0dHBzOi8vc
     2VydmVyLmV4YW1wbGUuY29tIiwiZXhwIjoxNjI1ODY5Njc3fQ.te4IdnP_DK4hWrh
     TWA6fyhy3fxlAQZAhfA4lmzRdpoP5uZb-E90R5YxzN1YDA8mnVdpgj_Bx1lG5r6se
     f5TlckApA3hahhC804dcqlE4naEmLISmN1pds2WxTMOUzZY8aKKSDzNTDqhyTgE-K
     dTb3RafRj7tdZb09zWs7c_moOvfVcQIoy5zz1BvLQKW1Y8JsYvdpu2AvpxRPbcP8W
     yeW9B6PL6_fy3pXYKG3e-qUcvPa9kan-mo9EoSgt-YTDQjK1nZMdXIqTluK9caVJE
     RWW0fD1Y11_tlOcJn-ya7v7d8YmFyJpkhZfm8x1FoeH0djEicXTixEkdRuzsgUCm6
     GQ

   The authorization server MUST process the request as follows:

   1.  Authenticate the client in the same way as at the token endpoint
       (Section 2.3 of [RFC6749]).

   2.  Reject the request if the "request_uri" authorization request
       parameter is provided.

   3.  Validate the pushed request as it would an authorization request
       sent to the authorization endpoint.  For example, the
       authorization server checks whether the redirect URI matches one
       of the redirect URIs configured for the client and also checks
       whether the client is authorized for the scope for which it is
       requesting access.  This validation allows the authorization
       server to refuse unauthorized or fraudulent requests early.  The
       authorization server MAY omit validation steps that it is unable
       to perform when processing the pushed request; however, such
       checks MUST then be performed when processing the authorization
       request at the authorization endpoint.

   The authorization server MAY allow clients with authentication
   credentials to establish per-authorization-request redirect URIs with
   every pushed authorization request.  Described in more detail in
   Section 2.4, this is possible since, in contrast to [RFC6749], this
   specification gives the authorization server the ability to
   authenticate clients and validate client requests before the actual
   authorization request is performed.

2.2.  Successful Response

   If the verification is successful, the server MUST generate a request
   URI and provide it in the response with a "201" HTTP status code.
   The following parameters are included as top-level members in the
   message body of the HTTP response using the "application/json" media
   type as defined by [RFC8259].

   request_uri
      The request URI corresponding to the authorization request posted.
      This URI is a single-use reference to the respective request data
      in the subsequent authorization request.  The way the
      authorization process obtains the authorization request data is at
      the discretion of the authorization server and is out of scope of
      this specification.  There is no need to make the authorization
      request data available to other parties via this URI.

   expires_in
      A JSON number that represents the lifetime of the request URI in
      seconds as a positive integer.  The request URI lifetime is at the
      discretion of the authorization server but will typically be
      relatively short (e.g., between 5 and 600 seconds).

   The format of the "request_uri" value is at the discretion of the
   authorization server, but it MUST contain some part generated using a
   cryptographically strong pseudorandom algorithm such that it is
   computationally infeasible to predict or guess a valid value (see
   Section 10.10 of [RFC6749] for specifics).  The authorization server
   MAY construct the "request_uri" value using the form
   "urn:ietf:params:oauth:request_uri:<reference-value>" with
   "<reference-value>" as the random part of the URI that references the
   respective authorization request data.

   The "request_uri" value MUST be bound to the client that posted the
   authorization request.

   The following is an example of such a response:

    HTTP/1.1 201 Created
    Content-Type: application/json
    Cache-Control: no-cache, no-store

    {
     "request_uri":
       "urn:ietf:params:oauth:request_uri:6esc_11ACC5bwc014ltc14eY22c",
     "expires_in": 60
    }

2.3.  Error Response

   The authorization server returns an error response with the same
   format as is specified for error responses from the token endpoint in
   Section 5.2 of [RFC6749] using the appropriate error code from
   therein or from Section 4.1.2.1 of [RFC6749].  In those cases where
   Section 4.1.2.1 of [RFC6749] prohibits automatic redirection with an
   error back to the requesting client and hence doesn't define an error
   code (for example, when the request fails due to a missing, invalid,
   or mismatching redirection URI), the "invalid_request" error code can
   be used as the default error code.  Error codes defined by the OAuth
   extension can also be used when such an extension is involved in the
   initial processing of the authorization request that was pushed.
   Since initial processing of the pushed authorization request does not
   involve resource owner interaction, error codes related to user
   interaction, such as "consent_required" defined by [OIDC], are never
   returned.

   If the client is required to use signed Request Objects, by either
   the authorization server or the client policy (see [RFC9101],
   Section 10.5), the authorization server MUST only accept requests
   complying with the definition given in Section 3 and MUST refuse any
   other request with HTTP status code 400 and error code
   "invalid_request".

   In addition to the above, the PAR endpoint can also make use of the
   following HTTP status codes:

   405:  If the request did not use the "POST" method, the authorization
         server responds with an HTTP 405 (Method Not Allowed) status
         code.

   413:  If the request size was beyond the upper bound that the
         authorization server allows, the authorization server responds
         with an HTTP 413 (Payload Too Large) status code.

   429:  If the number of requests from a client during a particular
         time period exceeds the number the authorization server allows,
         the authorization server responds with an HTTP 429 (Too Many
         Requests) status code.

   The following is an example of an error response from the PAR
   endpoint:

    HTTP/1.1 400 Bad Request
    Content-Type: application/json
    Cache-Control: no-cache, no-store

    {
      "error": "invalid_request",
      "error_description":
        "The redirect_uri is not valid for the given client"
    }

2.4.  Management of Client Redirect URIs

   OAuth 2.0 [RFC6749] allows clients to use unregistered "redirect_uri"
   values in certain circumstances or for the authorization server to
   apply its own matching semantics to the "redirect_uri" value
   presented by the client at the authorization endpoint.  However, the
   OAuth security BCP [OAUTH-SECURITY-TOPICS] as well as the OAuth 2.1
   specification [OAUTH-V2] require an authorization server to exactly
   match the "redirect_uri" parameter against the set of redirect URIs
   previously established for a particular client.  This is a means for
   early detection of client impersonation attempts and prevents token
   leakage and open redirection.  As a downside, this can make client
   management more cumbersome since the redirect URI is typically the
   most volatile part of a client policy.

   The exact matching requirement MAY be relaxed when using PAR for
   clients that have established authentication credentials with the
   authorization server.  This is possible since, in contrast to a
   conventional authorization request, the authorization server
   authenticates the client before the authorization process starts and
   thus ensures it is interacting with the legitimate client.  The
   authorization server MAY allow such clients to specify "redirect_uri"
   values that were not previously registered with the authorization
   server.  This will give the client more flexibility (e.g., to mint
   distinct "redirect_uri" values per authorization server at runtime)
   and can simplify client management.  It is at the discretion of the
   authorization server to apply restrictions on supplied "redirect_uri"
   values, e.g., the authorization server MAY require a certain URI
   prefix or allow only a query parameter to vary at runtime.

      |  Note: The ability to set up transaction-specific redirect URIs
      |  is also useful in situations where client IDs and corresponding
      |  credentials and policies are managed by a trusted third party,
      |  e.g., via client certificates containing client permissions.
      |  Such an externally managed client could interact with an
      |  authorization server trusting the respective third party
      |  without the need for an additional registration step.

3.  The "request" Request Parameter

   Clients MAY use the "request" parameter as defined in JAR [RFC9101]
   to push a Request Object JWT to the authorization server.  The rules
   for processing, signing, and encryption of the Request Object as
   defined in JAR [RFC9101] apply.  Request parameters required by a
   given client authentication method are included in the "application/
   x-www-form-urlencoded" request directly and are the only parameters
   other than "request" in the form body (e.g., mutual TLS client
   authentication [RFC8705] uses the "client_id" HTTP request parameter,
   while JWT assertion-based client authentication [RFC7523] uses
   "client_assertion" and "client_assertion_type").  All other request
   parameters, i.e., those pertaining to the authorization request
   itself, MUST appear as claims of the JWT representing the
   authorization request.

   The following is an example of a pushed authorization request using a
   signed Request Object with the same authorization request payload as
   the example in Section 2.1.  The client is authenticated with JWT
   client assertion-based authentication [RFC7523] (extra line breaks
   and spaces for display purposes only):

    POST /as/par HTTP/1.1
    Host: as.example.com
    Content-Type: application/x-www-form-urlencoded

    client_assertion_type=
     urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
    &client_assertion=eyJraWQiOiJrMmJkYyIsImFsZyI6IlJTMjU2In0.eyJpc3Mi
     OiJzNkJoZFJrcXQzIiwic3ViIjoiczZCaGRSa3F0MyIsImF1ZCI6Imh0dHBzOi8vc
     2VydmVyLmV4YW1wbGUuY29tIiwiZXhwIjoxNjI1ODY5Njc3fQ.te4IdnP_DK4hWrh
     TWA6fyhy3fxlAQZAhfA4lmzRdpoP5uZb-E90R5YxzN1YDA8mnVdpgj_Bx1lG5r6se
     f5TlckApA3hahhC804dcqlE4naEmLISmN1pds2WxTMOUzZY8aKKSDzNTDqhyTgE-K
     dTb3RafRj7tdZb09zWs7c_moOvfVcQIoy5zz1BvLQKW1Y8JsYvdpu2AvpxRPbcP8W
     yeW9B6PL6_fy3pXYKG3e-qUcvPa9kan-mo9EoSgt-YTDQjK1nZMdXIqTluK9caVJE
     RWW0fD1Y11_tlOcJn-ya7v7d8YmFyJpkhZfm8x1FoeH0djEicXTixEkdRuzsgUCm6
     GQ
    &request=eyJraWQiOiJrMmJkYyIsImFsZyI6IlJTMjU2In0.eyJpc3MiOiJzNkJoZ
     FJrcXQzIiwiYXVkIjoiaHR0cHM6Ly9zZXJ2ZXIuZXhhbXBsZS5jb20iLCJleHAiOj
     E2MjU4Njk2NzcsInJlc3BvbnNlX3R5cGUiOiJjb2RlIiwiY2xpZW50X2lkIjoiczZ
     CaGRSa3F0MyIsInJlZGlyZWN0X3VyaSI6Imh0dHBzOi8vY2xpZW50LmV4YW1wbGUu
     b3JnL2NiIiwic2NvcGUiOiJhY2NvdW50LWluZm9ybWF0aW9uIiwic3RhdGUiOiJhZ
     jBpZmpzbGRraiIsImNvZGVfY2hhbGxlbmdlIjoiSzItbHRjODNhY2M0aDBjOXc2RV
     NDX3JFTVRKM2J3dy11Q0hhb2VLMXQ4VSIsImNvZGVfY2hhbGxlbmdlX21ldGhvZCI
     6IlMyNTYifQ.l9R3RC9bFBHry_8acObQjEf4fX5yfJkWUPfak3J3iiBm0aaQznPw5
     BZ0B3VQZ9_KYdPt5bTkaflS5fSDklM3_7my9MyOSKFYmf46INk6ju_qUuC2crkOQX
     ZWYJB-0bnYEbdHpUjazFSUvN49cEGstNQeE-dKDWHNgEojgcuNA_pjKfL9VYp1dEA
     6-WjXZ_OlJ7R_mBWpjFAzc0UkQwqX5hfOJoGTqB2tE4a4aB2z8iYlUJp0DeeYp_hP
     N6svtmdvte73p5bLGDFpRIlmrBQIAQuxiS0skORpXlS0cBcgHimXVnXOJG7E-A_lS
     _5y54dVLQPA1jKYx-fxbYSG7dp2fw
    &client_id=s6BhdRkqt3

   The authorization server MUST take the following steps beyond the
   processing rules defined in Section 2.1:

   1.  If applicable, decrypt the Request Object as specified in JAR
       [RFC9101], Section 6.1.

   2.  Validate the Request Object signature as specified in JAR
       [RFC9101], Section 6.2.

   3.  If the client has authentication credentials established with the
       authorization server, reject the request if the authenticated
       "client_id" does not match the "client_id" claim in the Request
       Object.  Additionally, requiring the "iss" claim to match the
       "client_id" is at the discretion of the authorization server.

   The following RSA key pair, represented in JSON Web Key (JWK) format
   [RFC7517], can be used to validate or recreate the Request Object
   signature in the above example (extra line breaks and indentation
   within values for display purposes only):

    {
      "kty": "RSA",
      "kid":"k2bdc",
      "n": "y9Lqv4fCp6Ei-u2-ZCKq83YvbFEk6JMs_pSj76eMkddWRuWX2aBKGHAtKlE
            5P7_vn__PCKZWePt3vGkB6ePgzAFu08NmKemwE5bQI0e6kIChtt_6KzT5Oa
            aXDFI6qCLJmk51Cc4VYFaxgqevMncYrzaW_50mZ1yGSFIQzLYP8bijAHGVj
            dEFgZaZEN9lsn_GdWLaJpHrB3ROlS50E45wxrlg9xMncVb8qDPuXZarvghL
            L0HzOuYRadBJVoWZowDNTpKpk2RklZ7QaBO7XDv3uR7s_sf2g-bAjSYxYUG
            sqkNA9b3xVW53am_UZZ3tZbFTIh557JICWKHlWj5uzeJXaw",
      "e": "AQAB",
      "d": "LNwG_pCKrwowALpCpRdcOKlSVqylSurZhE6CpkRiE9cpDgGKIkO9CxPlXOL
            zjqxXuQc8MdMqRQZTnAwgd7HH0B6gncrruV3NewI-XQV0ckldTjqNfOTz1V
            Rs-jE-57KAXI3YBIhu-_0YpIDzdk_wBuAk661Svn0GsPQe7m9DoxdzenQu9
            O_soewUhlPzRrTH0EeIqYI715rwI3TYaSzoWBmEPD2fICyj18FF0MPy_SQz
            k3noVUUIzfzLnnJiWy_p63QBCMqjRoSHHdMnI4z9iVpIwJWQ3jO5n_2lC2-
            cSgwjmKsFzDBbQNJc7qMG1N6EssJUwgGJxz1eAUFf0w4YAQ",
      "qi": "J-mG0swR4FTy3atrcQ7dd0hhYn1E9QndN-
            -sDG4EQO0RnFj6wIefCvwIc4
            7hCtVeFnCTPYJNc_JyV-mU-9vlzS5GSNuyR5qdpsMZXUMpEvQcwKt23ffPZ
            YGaqfKyEesmf_Wi8fFcE68H9REQjnniKrXm7w2-IuG_IrVJA9Ox-uU",
      "q": "4hlMYAGa0dvogdK1jnxQ7J_Lqpqi99e-AeoFvoYpMPhthChTzwFZO9lQmUo
            BpMqVQTws_s7vWGmt7ZAB3ywkurf0pV7BD0fweJiUzrWk4KJjxtmP_auuxr
            jvm3s2FUGn6f0wRY9Z8Hj9A7C72DnYCjuZiJQMYCWDsZ8-d-L1a-s",
      "p": "5sd9Er3I2FFT9R-gy84_oakEyCmgw036B_nfYEEOCwpSvi2z7UcIVK3bSEL
            5WCW6BNgB3HDWhq8aYPirwQnqm0K9mX1E-4xM10WWZ-rP3XjYpQeS0Snru5
            LFVWsAzi-FX7BOqBibSAXLdEGXcXa44l08iec_bPD3xduq5V_1YoE",
      "dq": "Nz2PF3XM6bEc4XsluKZO70ErdYdKgdtIJReUR7Rno_tOZpejwlPGBYVW19
            zpAeYtCT82jxroB2XqhLxGeMxEPQpsz2qTKLSe4BgHY2ml2uxSDGdjcsrbb
            NoKUKaN1CuyZszhWl1n0AT_bENl4bJgQj_Fh0UEsQj5YBBUJt5gr_k",
      "dp": "Zc877jirkkLOtyTs2vxyNe9KnMNAmOidlUc2tE_-0gAL4Lpo1hSwKCtKwe
            ZJ-gkqt1hT-dwNx_0Xtg_-NXsadMRMwJnzBMYwYAfjApUkfqABc0yUCJJl3
            KozRCugf1WXkU9GZAH2_x8PUopdNUEa70ISowPRh04HANKX4fkjWAE"
     }

4.  Authorization Request

   The client uses the "request_uri" value returned by the authorization
   server to build an authorization request as defined in [RFC9101].
   This is shown in the following example where the client directs the
   user agent to make the following HTTP request (extra line breaks and
   indentation for display purposes only):

    GET /authorize?client_id=s6BhdRkqt3&request_uri=urn%3Aietf%3Aparams
     %3Aoauth%3Arequest_uri%3A6esc_11ACC5bwc014ltc14eY22c HTTP/1.1
    Host: as.example.com

   Since parts of the authorization request content, e.g., the
   "code_challenge" parameter value, are unique to a particular
   authorization request, the client MUST only use a "request_uri" value
   once.  Authorization servers SHOULD treat "request_uri" values as
   one-time use but MAY allow for duplicate requests due to a user
   reloading/refreshing their user agent.  An expired "request_uri" MUST
   be rejected as invalid.

   The authorization server MUST validate authorization requests arising
   from a pushed request as it would any other authorization request.
   The authorization server MAY omit validation steps that it performed
   when the request was pushed, provided that it can validate that the
   request was a pushed request and that the request or the
   authorization server's policy has not been modified in a way that
   would affect the outcome of the omitted steps.

   Authorization server policy MAY dictate, either globally or on a per-
   client basis, that PAR be the only means for a client to pass
   authorization request data.  In this case, the authorization server
   will refuse, using the "invalid_request" error code, to process any
   request to the authorization endpoint that does not have a
   "request_uri" parameter with a value obtained from the PAR endpoint.

      |  Note: Authorization server and clients MAY use metadata as
      |  defined in Sections 5 and 6 to signal the desired behavior.

5.  Authorization Server Metadata

   The following authorization server metadata parameters [RFC8414] are
   introduced to signal the server's capability and policy with respect
   to PAR.

   pushed_authorization_request_endpoint
      The URL of the pushed authorization request endpoint at which a
      client can post an authorization request to exchange for a
      "request_uri" value usable at the authorization server.

   require_pushed_authorization_requests
      Boolean parameter indicating whether the authorization server
      accepts authorization request data only via PAR.  If omitted, the
      default value is "false".

   Note that the presence of "pushed_authorization_request_endpoint" is
   sufficient for a client to determine that it may use the PAR flow.  A
   "request_uri" value obtained from the PAR endpoint is usable at the
   authorization endpoint regardless of other authorization server
   metadata such as "request_uri_parameter_supported" or
   "require_request_uri_registration" [OIDC.Disco].

6.  Client Metadata

   The Dynamic Client Registration Protocol [RFC7591] defines an API for
   dynamically registering OAuth 2.0 client metadata with authorization
   servers.  The metadata defined by [RFC7591], and registered
   extensions to it, also imply a general data model for clients that is
   useful for authorization server implementations even when the Dynamic
   Client Registration Protocol isn't in play.  Such implementations
   will typically have some sort of user interface available for
   managing client configuration.  The following client metadata
   parameter is introduced by this document to indicate whether pushed
   authorization requests are required for the given client.

   require_pushed_authorization_requests
      Boolean parameter indicating whether the only means of initiating
      an authorization request the client is allowed to use is PAR.  If
      omitted, the default value is "false".

7.  Security Considerations

7.1.  Request URI Guessing

   An attacker could attempt to guess and replay a valid request URI
   value and try to impersonate the respective client.  The
   authorization server MUST account for the considerations given in JAR
   [RFC9101], Section 10.2, clause (d) on request URI entropy.

7.2.  Open Redirection

   An attacker could try to register a redirect URI pointing to a site
   under their control in order to obtain authorization codes or launch
   other attacks towards the user.  The authorization server MUST only
   accept new redirect URIs in the pushed authorization request from
   authenticated clients.

7.3.  Request Object Replay

   An attacker could replay a request URI captured from a legitimate
   authorization request.  In order to cope with such attacks, the
   authorization server SHOULD make the request URIs one-time use.

7.4.  Client Policy Change

   The client policy might change between the lodging of the Request
   Object and the authorization request using a particular Request
   Object.  Therefore, it is recommended that the authorization server
   check the request parameter against the client policy when processing
   the authorization request.

7.5.  Request URI Swapping

   An attacker could capture the request URI from one request and then
   substitute it into a different authorization request.  For example,
   in the context of OpenID Connect, an attacker could replace a request
   URI asking for a high level of authentication assurance with one that
   requires a lower level of assurance.  Clients SHOULD make use of PKCE
   [RFC7636], a unique "state" parameter [RFC6749], or the OIDC "nonce"
   parameter [OIDC] in the pushed Request Object to prevent this attack.

8.  Privacy Considerations

   OAuth 2.0 is a complex and flexible framework with broad-ranging
   privacy implications due to its very nature of having one entity
   intermediate user authorization to data access between two other
   entities.  The privacy considerations of all of OAuth are beyond the
   scope of this document, which only defines an alternative way of
   initiating one message sequence in the larger framework.  However,
   using PAR may improve privacy by reducing the potential for
   inadvertent information disclosure since it passes the authorization
   request data directly between the client and authorization server
   over a secure connection in the message body of an HTTP request
   rather than in the query component of a URL that passes through the
   user agent in the clear.

9.  IANA Considerations

9.1.  OAuth Authorization Server Metadata

   IANA has registered the following values in the IANA "OAuth
   Authorization Server Metadata" registry of [IANA.OAuth.Parameters]
   established by [RFC8414].

   Metadata Name:  "pushed_authorization_request_endpoint"
   Metadata Description:  URL of the authorization server's pushed
      authorization request endpoint.
   Change Controller:  IESG
   Specification Document(s):  Section 5 of RFC 9126

   Metadata Name:  "require_pushed_authorization_requests"
   Metadata Description:  Indicates whether the authorization server
      accepts authorization requests only via PAR.
   Change Controller:  IESG
   Specification Document(s):  Section 5 of RFC 9126

9.2.  OAuth Dynamic Client Registration Metadata

   IANA has registered the following value in the IANA "OAuth Dynamic
   Client Registration Metadata" registry of [IANA.OAuth.Parameters]
   established by [RFC7591].

   Client Metadata Name:  "require_pushed_authorization_requests"
   Client Metadata Description:  Indicates whether the client is
      required to use PAR to initiate authorization requests.
   Change Controller:  IESG
   Specification Document(s):  Section 6 of RFC 9126

9.3.  OAuth URI Registration

   IANA has registered the following value in the "OAuth URI" registry
   of [IANA.OAuth.Parameters] established by [RFC6755].

   URN:  "urn:ietf:params:oauth:request_uri:"
   Common Name:  A URN Sub-Namespace for OAuth Request URIs.
   Change Controller:  IESG
   Specification Document(s):  Section 2.2 of RFC 9126

10.  References

10.1.  Normative References

   [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>.

   [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>.

   [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>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [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>.

   [RFC9101]  Sakimura, N., Bradley, J., and M. Jones, "The OAuth 2.0
              Authorization Framework: JWT-Secured Authorization Request
              (JAR)", RFC 9101, DOI 10.17487/RFC9101, August 2021,
              <https://www.rfc-editor.org/info/rfc9101>.

10.2.  Informative References

   [IANA.OAuth.Parameters]
              IANA, "OAuth Parameters",
              <http://www.iana.org/assignments/oauth-parameters>.

   [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-18, 13 April 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-oauth-
              security-topics-18>.

   [OAUTH-V2] Hardt, D., Parecki, A., and T. Lodderstedt, "The OAuth 2.1
              Authorization Framework", Work in Progress, Internet-
              Draft, draft-ietf-oauth-v2-1-03, 8 September 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-oauth-
              v2-1-03>.

   [OIDC]     Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
              C. Mortimore, "OpenID Connect Core 1.0 incorporating
              errata set 1", November 2014,
              <http://openid.net/specs/openid-connect-core-1_0.html>.

   [OIDC.Disco]
              Sakimura, N., Bradley, J., Jones, M., and E. Jay, "OpenID
              Connect Discovery 1.0 incorporating errata set 1",
              November 2014, <http://openid.net/specs/openid-connect-
              discovery-1_0.html>.

   [RFC6755]  Campbell, B. and H. Tschofenig, "An IETF URN Sub-Namespace
              for OAuth", RFC 6755, DOI 10.17487/RFC6755, October 2012,
              <https://www.rfc-editor.org/info/rfc6755>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <https://www.rfc-editor.org/info/rfc7517>.

   [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>.

   [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/info/rfc7523>.

   [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>.

   [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>.

   [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>.

   [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>.

Acknowledgements

   This specification is based on the work on Pushed Request Object
   (https://bitbucket.org/openid/fapi/src/master/
   Financial_API_Pushed_Request_Object.md) conducted at the Financial-
   grade API Working Group at the OpenID Foundation.  We would like to
   thank the members of the WG for their valuable contributions.

   We would like to thank Vladimir Dzhuvinov, Aaron Parecki, Justin
   Richer, Sascha Preibisch, Daniel Fett, Michael B. Jones, Annabelle
   Backman, Joseph Heenan, Sean Glencross, Maggie Hung, Neil Madden,
   Karsten Meyer zu Selhausen, Roman Danyliw, Meral Shirazipour, and
   Takahiko Kawasaki for their valuable feedback on this document.

Authors' Addresses

   Torsten Lodderstedt
   yes.com

   Email: torsten@lodderstedt.net

   Brian Campbell
   Ping Identity

   Email: bcampbell@pingidentity.com

   Nat Sakimura
   NAT.Consulting

   Email: nat@sakimura.org

   Dave Tonge
   Moneyhub Financial Technology

   Email: dave@tonge.org

   Filip Skokan
   Auth0

   Email: panva.ip@gmail.com