OAuth JWT Profile: JSON Web Token (JWT) Profile for OAuth 2.0 Client Authentication and Authorization Grants

Internet Engineering Task Force (IETF)                          M. Jones
Request for Comments: 7523                                     Microsoft
Category: Standards Track                                    B. Campbell
ISSN: 2070-1721                                            Ping Identity
                                                            C. Mortimore
                                                              Salesforce
                                                                May 2015


                      JSON Web Token (JWT) Profile
      for OAuth 2.0 Client Authentication and Authorization Grants

Abstract

   This specification defines the use of a JSON Web Token (JWT) Bearer
   Token as a means for requesting an OAuth 2.0 access token as well as
   for client authentication.

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 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7523.

Copyright Notice

   Copyright (c) 2015 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
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   publication of this document.  Please review these documents
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  HTTP Parameter Bindings for Transporting Assertions . . . . .   4
     2.1.  Using JWTs as Authorization Grants  . . . . . . . . . . .   4
     2.2.  Using JWTs for Client Authentication  . . . . . . . . . .   5
   3.  JWT Format and Processing Requirements  . . . . . . . . . . .   5
     3.1.  Authorization Grant Processing  . . . . . . . . . . . . .   7
     3.2.  Client Authentication Processing  . . . . . . . . . . . .   8
   4.  Authorization Grant Example . . . . . . . . . . . . . . . . .   8
   5.  Interoperability Considerations . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  10
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Sub-Namespace Registration of
           urn:ietf:params:oauth:grant-type:jwt-bearer . . . . . . .  10
     8.2.  Sub-Namespace Registration of
           urn:ietf:params:oauth:client-assertion-type:jwt-bearer  .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   JSON Web Token (JWT) [JWT] is a JSON-based [RFC7159] security token
   encoding that enables identity and security information to be shared
   across security domains.  A security token is generally issued by an
   Identity Provider and consumed by a Relying Party that relies on its
   content to identify the token's subject for security-related
   purposes.

   The OAuth 2.0 Authorization Framework [RFC6749] provides a method for
   making authenticated HTTP requests to a resource using an access
   token.  Access tokens are issued to third-party clients by an
   authorization server (AS) with the (sometimes implicit) approval of
   the resource owner.  In OAuth, an authorization grant is an abstract
   term used to describe intermediate credentials that represent the
   resource owner authorization.  An authorization grant is used by the
   client to obtain an access token.  Several authorization grant types
   are defined to support a wide range of client types and user
   experiences.  OAuth also allows for the definition of new extension
   grant types to support additional clients or to provide a bridge
   between OAuth and other trust frameworks.  Finally, OAuth allows the
   definition of additional authentication mechanisms to be used by
   clients when interacting with the authorization server.

   "Assertion Framework for OAuth 2.0 Client Authentication and
   Authorization Grants" [RFC7521] is an abstract extension to OAuth 2.0
   that provides a general framework for the use of assertions (a.k.a.
   security tokens) as client credentials and/or authorization grants
   with OAuth 2.0.  This specification profiles the OAuth Assertion
   Framework [RFC7521] to define an extension grant type that uses a JWT
   Bearer Token to request an OAuth 2.0 access token as well as for use
   as client credentials.  The format and processing rules for the JWT
   defined in this specification are intentionally similar, though not
   identical, to those in the closely related specification "Security
   Assertion Markup Language (SAML) 2.0 Profile for OAuth 2.0 Client
   Authentication and Authorization Grants" [RFC7522].  The differences
   arise where the structure and semantics of JWTs differ from SAML
   Assertions.  JWTs, for example, have no direct equivalent to the
   <SubjectConfirmation> or <AuthnStatement> elements of SAML
   Assertions.

   This document defines how a JWT Bearer Token can be used to request
   an access token when a client wishes to utilize an existing trust
   relationship, expressed through the semantics of the JWT, without a
   direct user-approval step at the authorization server.  It also
   defines how a JWT can be used as a client authentication mechanism.
   The use of a security token for client authentication is orthogonal
   to and separable from using a security token as an authorization
   grant.  They can be used either in combination or separately.  Client
   authentication using a JWT is nothing more than an alternative way
   for a client to authenticate to the token endpoint and must be used
   in conjunction with some grant type to form a complete and meaningful
   protocol request.  JWT authorization grants may be used with or
   without client authentication or identification.  Whether or not
   client authentication is needed in conjunction with a JWT
   authorization grant, as well as the supported types of client
   authentication, are policy decisions at the discretion of the
   authorization server.

   The process by which the client obtains the JWT, prior to exchanging
   it with the authorization server or using it for client
   authentication, is out of scope.

1.1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   Unless otherwise noted, all the protocol parameter names and values
   are case sensitive.

1.2.  Terminology

   All terms are as defined in the following specifications: "The OAuth
   2.0 Authorization Framework" [RFC6749], the OAuth Assertion Framework
   [RFC7521], and "JSON Web Token (JWT)" [JWT].

2.  HTTP Parameter Bindings for Transporting Assertions

   The OAuth Assertion Framework [RFC7521] defines generic HTTP
   parameters for transporting assertions (a.k.a. security tokens)
   during interactions with a token endpoint.  This section defines
   specific parameters and treatments of those parameters for use with
   JWT Bearer Tokens.

2.1.  Using JWTs as Authorization Grants

   To use a Bearer JWT as an authorization grant, the client uses an
   access token request as defined in Section 4 of the OAuth Assertion
   Framework [RFC7521] with the following specific parameter values and
   encodings.

   The value of the "grant_type" is "urn:ietf:params:oauth:grant-
   type:jwt-bearer".

   The value of the "assertion" parameter MUST contain a single JWT.

   The "scope" parameter may be used, as defined in the OAuth Assertion
   Framework [RFC7521], to indicate the requested scope.

   Authentication of the client is optional, as described in
   Section 3.2.1 of OAuth 2.0 [RFC6749] and consequently, the
   "client_id" is only needed when a form of client authentication that
   relies on the parameter is used.

   The following example demonstrates an access token request with a JWT
   as an authorization grant (with extra line breaks for display
   purposes only):

     POST /token.oauth2 HTTP/1.1
     Host: as.example.com
     Content-Type: application/x-www-form-urlencoded

     grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer
     &assertion=eyJhbGciOiJFUzI1NiIsImtpZCI6IjE2In0.
     eyJpc3Mi[...omitted for brevity...].
     J9l-ZhwP[...omitted for brevity...]

2.2.  Using JWTs for Client Authentication

   To use a JWT Bearer Token for client authentication, the client uses
   the following parameter values and encodings.

   The value of the "client_assertion_type" is
   "urn:ietf:params:oauth:client-assertion-type:jwt-bearer".

   The value of the "client_assertion" parameter contains a single JWT.
   It MUST NOT contain more than one JWT.

   The following example demonstrates client authentication using a JWT
   during the presentation of an authorization code grant in an access
   token request (with extra line breaks for display purposes only):

     POST /token.oauth2 HTTP/1.1
     Host: as.example.com
     Content-Type: application/x-www-form-urlencoded

     grant_type=authorization_code&
     code=n0esc3NRze7LTCu7iYzS6a5acc3f0ogp4&
     client_assertion_type=urn%3Aietf%3Aparams%3Aoauth%3A
     client-assertion-type%3Ajwt-bearer&
     client_assertion=eyJhbGciOiJSUzI1NiIsImtpZCI6IjIyIn0.
     eyJpc3Mi[...omitted for brevity...].
     cC4hiUPo[...omitted for brevity...]

3.  JWT Format and Processing Requirements

   In order to issue an access token response as described in OAuth 2.0
   [RFC6749] or to rely on a JWT for client authentication, the
   authorization server MUST validate the JWT according to the criteria
   below.  Application of additional restrictions and policy are at the
   discretion of the authorization server.

   1.   The JWT MUST contain an "iss" (issuer) claim that contains a
        unique identifier for the entity that issued the JWT.  In the
        absence of an application profile specifying otherwise,
        compliant applications MUST compare issuer values using the
        Simple String Comparison method defined in Section 6.2.1 of RFC
        3986 [RFC3986].

   2.   The JWT MUST contain a "sub" (subject) claim identifying the
        principal that is the subject of the JWT.  Two cases need to be
        differentiated:

        A.  For the authorization grant, the subject typically
            identifies an authorized accessor for which the access token
            is being requested (i.e., the resource owner or an
            authorized delegate), but in some cases, may be a
            pseudonymous identifier or other value denoting an anonymous
            user.

        B.  For client authentication, the subject MUST be the
            "client_id" of the OAuth client.

   3.   The JWT MUST contain an "aud" (audience) claim containing a
        value that identifies the authorization server as an intended
        audience.  The token endpoint URL of the authorization server
        MAY be used as a value for an "aud" element to identify the
        authorization server as an intended audience of the JWT.  The
        authorization server MUST reject any JWT that does not contain
        its own identity as the intended audience.  In the absence of an
        application profile specifying otherwise, compliant applications
        MUST compare the audience values using the Simple String
        Comparison method defined in Section 6.2.1 of RFC 3986
        [RFC3986].  As noted in Section 5, the precise strings to be
        used as the audience for a given authorization server must be
        configured out of band by the authorization server and the
        issuer of the JWT.

   4.   The JWT MUST contain an "exp" (expiration time) claim that
        limits the time window during which the JWT can be used.  The
        authorization server MUST reject any JWT with an expiration time
        that has passed, subject to allowable clock skew between
        systems.  Note that the authorization server may reject JWTs
        with an "exp" claim value that is unreasonably far in the
        future.

   5.   The JWT MAY contain an "nbf" (not before) claim that identifies
        the time before which the token MUST NOT be accepted for
        processing.

   6.   The JWT MAY contain an "iat" (issued at) claim that identifies
        the time at which the JWT was issued.  Note that the
        authorization server may reject JWTs with an "iat" claim value
        that is unreasonably far in the past.

   7.   The JWT MAY contain a "jti" (JWT ID) claim that provides a
        unique identifier for the token.  The authorization server MAY
        ensure that JWTs are not replayed by maintaining the set of used
        "jti" values for the length of time for which the JWT would be
        considered valid based on the applicable "exp" instant.

   8.   The JWT MAY contain other claims.

   9.   The JWT MUST be digitally signed or have a Message
        Authentication Code (MAC) applied by the issuer.  The
        authorization server MUST reject JWTs with an invalid signature
        or MAC.

   10.  The authorization server MUST reject a JWT that is not valid in
        all other respects per "JSON Web Token (JWT)" [JWT].

3.1.  Authorization Grant Processing

   JWT authorization grants may be used with or without client
   authentication or identification.  Whether or not client
   authentication is needed in conjunction with a JWT authorization
   grant, as well as the supported types of client authentication, are
   policy decisions at the discretion of the authorization server.
   However, if client credentials are present in the request, the
   authorization server MUST validate them.

   If the JWT is not valid, or the current time is not within the
   token's valid time window for use, the authorization server
   constructs an error response as defined in OAuth 2.0 [RFC6749].  The
   value of the "error" parameter MUST be the "invalid_grant" error
   code.  The authorization server MAY include additional information
   regarding the reasons the JWT was considered invalid using the
   "error_description" or "error_uri" parameters.

   For example:

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

     {
      "error":"invalid_grant",
      "error_description":"Audience validation failed"
     }

3.2.  Client Authentication Processing

   If the client JWT is not valid, the authorization server constructs
   an error response as defined in OAuth 2.0 [RFC6749].  The value of
   the "error" parameter MUST be the "invalid_client" error code.  The
   authorization server MAY include additional information regarding the
   reasons the JWT was considered invalid using the "error_description"
   or "error_uri" parameters.

4.  Authorization Grant Example

   The following examples illustrate what a conforming JWT and an access
   token request would look like.

   The example shows a JWT issued and signed by the system entity
   identified as "https://jwt-idp.example.com".  The subject of the JWT
   is identified by email address as "mike@example.com".  The intended
   audience of the JWT is "https://jwt-rp.example.net", which is an
   identifier with which the authorization server identifies itself.
   The JWT is sent as part of an access token request to the
   authorization server's token endpoint at "https://authz.example.net/
   token.oauth2".

   Below is an example JSON object that could be encoded to produce the
   JWT Claims Set for a JWT:

     {"iss":"https://jwt-idp.example.com",
      "sub":"mailto:mike@example.com",
      "aud":"https://jwt-rp.example.net",
      "nbf":1300815780,
      "exp":1300819380,
      "http://claims.example.com/member":true}

   The following example JSON object, used as the header of a JWT,
   declares that the JWT is signed with the Elliptic Curve Digital
   Signature Algorithm (ECDSA) P-256 SHA-256 using a key identified by
   the "kid" value "16".

     {"alg":"ES256","kid":"16"}

   To present the JWT with the claims and header shown in the previous
   example as part of an access token request, for example, the client
   might make the following HTTPS request (with extra line breaks for
   display purposes only):

     POST /token.oauth2 HTTP/1.1
     Host: authz.example.net
     Content-Type: application/x-www-form-urlencoded

     grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer
     &assertion=eyJhbGciOiJFUzI1NiIsImtpZCI6IjE2In0.
     eyJpc3Mi[...omitted for brevity...].
     J9l-ZhwP[...omitted for brevity...]

5.  Interoperability Considerations

   Agreement between system entities regarding identifiers, keys, and
   endpoints is required in order to achieve interoperable deployments
   of this profile.  Specific items that require agreement are as
   follows: values for the issuer and audience identifiers, the location
   of the token endpoint, the key used to apply and verify the digital
   signature or MAC over the JWT, one-time use restrictions on the JWT,
   maximum JWT lifetime allowed, and the specific subject and claim
   requirements of the JWT.  The exchange of such information is
   explicitly out of scope for this specification.  In some cases,
   additional profiles may be created that constrain or prescribe these
   values or specify how they are to be exchanged.  Examples of such
   profiles include the OAuth 2.0 Dynamic Client Registration Core
   Protocol [OAUTH-DYN-REG], OpenID Connect Dynamic Client Registration
   1.0 [OpenID.Registration], and OpenID Connect Discovery 1.0
   [OpenID.Discovery].

   The "RS256" algorithm, from [JWA], is a mandatory-to-implement JSON
   Web Signature algorithm for this profile.

6.  Security Considerations

   The security considerations described within the following
   specifications are all applicable to this document: "Assertion
   Framework for OAuth 2.0 Client Authentication and Authorization
   Grants" [RFC7521], "The OAuth 2.0 Authorization Framework" [RFC6749],
   and "JSON Web Token (JWT)" [JWT].

   The specification does not mandate replay protection for the JWT
   usage for either the authorization grant or for client
   authentication.  It is an optional feature, which implementations may
   employ at their own discretion.

7.  Privacy Considerations

   A JWT may contain privacy-sensitive information and, to prevent
   disclosure of such information to unintended parties, should only be
   transmitted over encrypted channels, such as Transport Layer Security
   (TLS).  In cases where it is desirable to prevent disclosure of
   certain information to the client, the JWT should be encrypted to the
   authorization server.

   Deployments should determine the minimum amount of information
   necessary to complete the exchange and include only such claims in
   the JWT.  In some cases, the "sub" (subject) claim can be a value
   representing an anonymous or pseudonymous user, as described in
   Section 6.3.1 of the OAuth Assertion Framework [RFC7521].

8.  IANA Considerations

8.1.  Sub-Namespace Registration of
      urn:ietf:params:oauth:grant-type:jwt-bearer

   This section registers the value "grant-type:jwt-bearer" in the IANA
   "OAuth URI" registry established by "An IETF URN Sub-Namespace for
   OAuth" [RFC6755].

   o  URN: urn:ietf:params:oauth:grant-type:jwt-bearer
   o  Common Name: JWT Bearer Token Grant Type Profile for OAuth 2.0
   o  Change Controller: IESG
   o  Specification Document: RFC 7523

8.2.  Sub-Namespace Registration of
      urn:ietf:params:oauth:client-assertion-type:jwt-bearer

   This section registers the value "client-assertion-type:jwt-bearer"
   in the IANA "OAuth URI" registry established by "An IETF URN Sub-
   Namespace for OAuth" [RFC6755].

   o  URN: urn:ietf:params:oauth:client-assertion-type:jwt-bearer
   o  Common Name: JWT Bearer Token Profile for OAuth 2.0 Client
      Authentication
   o  Change Controller: IESG
   o  Specification Document: RFC 7523

9.  References

9.1.  Normative References

   [JWA]      Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <http://www.rfc-editor.org/info/rfc7518>.

   [JWT]      Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <http://www.rfc-editor.org/info/rfc7519>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [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,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <http://www.rfc-editor.org/info/rfc6749>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <http://www.rfc-editor.org/info/rfc7159>.

   [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, <http://www.rfc-editor.org/info/rfc7521>.

9.2.  Informative References

   [OAUTH-DYN-REG]
              Richer, J., Jones, M., Bradley, J., Machulak, M., and P.
              Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
              Work in Progress, draft-ietf-oauth-dyn-reg-29, May 2015.

   [OpenID.Discovery]
              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>.

   [OpenID.Registration]
              Sakimura, N., Bradley, J., and M. Jones, "OpenID Connect
              Dynamic Client Registration 1.0 incorporating errata set
              1", November 2014, <http://openid.net/specs/
              openid-connect-registration-1_0.html>.

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

   [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,
              <http://www.rfc-editor.org/info/rfc7522>.

Acknowledgements

   This profile was derived from "Security Assertion Markup Language
   (SAML) 2.0 Profile for OAuth 2.0 Client Authentication and
   Authorization Grants" [RFC7522], which has the same authors as this
   document.

Authors' Addresses

   Michael B. Jones
   Microsoft

   EMail: mbj@microsoft.com
   URI:   http://self-issued.info/


   Brian Campbell
   Ping Identity

   EMail: brian.d.campbell@gmail.com


   Chuck Mortimore
   Salesforce

   EMail: cmortimore@salesforce.com