JSON Web Token (JWT) Profile for OAuth 2.0 Client Authentication and Authorization Grants
draft-ietf-oauth-jwt-bearer-12

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 use as a means of client authentication.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on May 16, 2015.

Copyright Notice

Copyright (c) 2014 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 (http://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. Notational Conventions
• 1.2. Terminology
• 2. HTTP Parameter Bindings for Transporting Assertions
• 2.1. Using JWTs as Authorization Grants
• 2.2. Using JWTs for Client Authentication
• 3. JWT Format and Processing Requirements
• 3.1. Authorization Grant Processing
• 3.2. Client Authentication Processing
• 4. Authorization Grant Example
• 5. Interoperability Considerations
• 6. Security Considerations
• 7. Privacy Considerations
• 8. IANA Considerations
• 8.1. Sub-Namespace Registration of urn:ietf:params:oauth:grant-type:jwt-bearer
• 8.2. Sub-Namespace Registration of urn:ietf:params:oauth:client-assertion-type:jwt-bearer
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Appendix A. Acknowledgements
• Appendix B. Document History
• Authors' Addresses

1. Introduction

JSON Web Token (JWT) [JWT] is a JavaScript Object Notation (JSON) [RFC7159] based 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.

The Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants [I-D.ietf-oauth-assertions] specification 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 Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants [I-D.ietf-oauth-assertions] specification to define an extension grant type that uses a JSON Web Token (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 SAML 2.0 Profile for OAuth 2.0 Client Authentication and Authorization Grants [I-D.ietf-oauth-saml2-bearer] specification. 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 JSON Web Token (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 (and digital signature or Message Authentication Code calculated over) 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 OAuth 2.0 Authorization Framework [RFC6749], the Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants [I-D.ietf-oauth-assertions], and the JSON Web Token (JWT) [JWT] specifications.

2. HTTP Parameter Bindings for Transporting Assertions

The Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants [I-D.ietf-oauth-assertions] specification 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 Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants [I-D.ietf-oauth-assertions] specification 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 Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants [I-D.ietf-oauth-assertions] specification, 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=eyJhbGciOiJFUzI1NiJ9.
  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=vAZEIHjQTHuGgaSvyW9hO0RpusLzkvTOww3trZBxZpo&
  client_assertion_type=urn%3Aietf%3Aparams%3Aoauth%3A
  client-assertion-type%3Ajwt-bearer&
  client_assertion=eyJhbGciOiJSUzI1NiJ9.
  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:
   1. 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.
   2. 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) 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 applied by the issuer. The authorization server MUST reject JWTs with an invalid signature or Message Authentication Code.
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 Object 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 ECDSA P-256 SHA-256 algorithm.

  {"alg":"ES256"}

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=eyJhbGciOiJFUzI1NiJ9.
  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 Message Authentication Code 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 [I-D.ietf-oauth-dyn-reg], OpenID Connect Dynamic Client Registration 1.0 [OpenID.Registration], and OpenID Connect Discovery 1.0 [OpenID.Discovery].

The RS256 algorithm, from [I-D.ietf-jose-json-web-algorithms], is a mandatory to implement JSON Web Signature algorithm for this profile.

6. Security Considerations

The security considerations described within the Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants [I-D.ietf-oauth-assertions], The OAuth 2.0 Authorization Framework [RFC6749], and the JSON Web Token (JWT) [JWT] specifications are all applicable to this document.

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 TLS. In cases where it is desirable to prevent disclosure of certain information to the client, the JWT should be 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 Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants [I-D.ietf-oauth-assertions].

8. IANA Considerations

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

This specification registers the value grant-type:jwt-bearer in the IANA urn:ietf:params:oauth registry established in An IETF URN Sub-Namespace for OAuth [RFC6755].

• URN: urn:ietf:params:oauth:grant-type:jwt-bearer
• Common Name: JWT Bearer Token Grant Type Profile for OAuth 2.0
• Change controller: IESG
• Specification Document: [[this document]]

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

This specification registers the value client-assertion-type:jwt-bearer in the IANA urn:ietf:params:oauth registry established in An IETF URN Sub-Namespace for OAuth [RFC6755].

• URN: urn:ietf:params:oauth:client-assertion-type:jwt-bearer
• Common Name: JWT Bearer Token Profile for OAuth 2.0 Client Authentication
• Change controller: IESG
• Specification Document: [[this document]]

9. References

9.1. Normative References

9.2. Informative References

Appendix A. Acknowledgements

This profile was derived from SAML 2.0 Profile for OAuth 2.0 Client Authentication and Authorization Grants [I-D.ietf-oauth-saml2-bearer] by Brian Campbell and Chuck Mortimore.

Appendix B. Document History

[[ to be removed by the RFC editor before publication as an RFC ]]

draft-ietf-oauth-jwt-bearer-12

• Fix typo per http://www.ietf.org/mail-archive/web/oauth/current/msg13790.html

draft-ietf-oauth-jwt-bearer-11

• Changes/suggestions from IESG reviews.

draft-ietf-oauth-jwt-bearer-10

• Added Privacy Considerations section per AD review discussion http://www.ietf.org/mail-archive/web/oauth/current/msg13148.html and http://www.ietf.org/mail-archive/web/oauth/current/msg13144.html

draft-ietf-oauth-jwt-bearer-09

• Clarified some text around the treatment of subject based on the rough rough consensus from the thread staring at http://www.ietf.org/mail-archive/web/oauth/current/msg12630.html

draft-ietf-oauth-jwt-bearer-08

• Updated references, including replacing references to RFC 4627 with RFC 7159.

draft-ietf-oauth-jwt-bearer-07

• Clean up language around subject per http://www.ietf.org/mail-archive/web/oauth/current/msg12250.html.
• As suggested in http://www.ietf.org/mail-archive/web/oauth/current/msg12251.html stated that "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."
• Added one-time use, maximum lifetime, and specific subject and attribute requirements to Interoperability Considerations based on http://www.ietf.org/mail-archive/web/oauth/current/msg12252.html.
• Remove "or its subject confirmation requirements cannot be met" text.
• Reword security considerations and mention that replay protection is not mandated based on http://www.ietf.org/mail-archive/web/oauth/current/msg12259.html.

-06

• Stated that issuer and audience values SHOULD be compared using the Simple String Comparison method defined in Section 6.2.1 of RFC 3986 unless otherwise specified by the application.

-05

• Changed title from "JSON Web Token (JWT) Bearer Token Profiles for OAuth 2.0" to "JSON Web Token (JWT) Profile for OAuth 2.0 Client Authentication and Authorization Grants" to be more explicit about the scope of the document per http://www.ietf.org/mail-archive/web/oauth/current/msg11063.html.
• Numbered the list of processing rules.
• Smallish editorial cleanups to try and improve readability and comprehensibility.
• Cleaner split out of the processing rules in cases where they differ for client authentication and authorization grants.
• Clarified the parameters that are used/available for authorization grants.
• Added Interoperability Considerations section.
• Added more explanatory context to the example in Section 4.

-04

• Changed the name of the prn claim to sub (subject) both to more closely align with SAML name usage and to use a more intuitive name.
• Added seriesInfo information to Internet Draft references.

-03

• Reference RFC 6749 and RFC 6755.

-02

• Add more text to intro explaining that an assertion/JWT grant type can be used with or without client authentication/identification and that client assertion/JWT authentication is nothing more than an alternative way for a client to authenticate to the token endpoint
• Add examples to Sections 2.1 and 2.2
• Update references

-01

• Tracked specification name changes: "The OAuth 2.0 Authorization Protocol" to "The OAuth 2.0 Authorization Framework" and "OAuth 2.0 Assertion Profile" to "Assertion Framework for OAuth 2.0".
• Merged in changes between draft-ietf-oauth-saml2-bearer-11 and draft-ietf-oauth-saml2-bearer-13. All changes were strictly editorial.

-00

• Created the initial IETF draft based upon draft-jones-oauth-jwt-bearer-04 with no normative changes.

Authors' Addresses