OAuth Working Group N. Sakimura
Internet-Draft Nomura Research Institute
Intended status: Standards Track March 26, 2015
Expires: September 27, 2015

Sender Constrained JWT for OAuth 2.0


This discussion document describes a method to indicate a sender constraint within JWT. It could potentially be incorporated into POP spec.

Requirements Language

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].

Status of This Memo

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This Internet-Draft will expire on September 27, 2015.

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Table of Contents

1. Introduction

OAuth 2.0 Proof-of-Possession (PoP) Security Architecture [POPA] identifies Sender Constraint and Key Confirmation as a possible threat mitigation against the use of token by an unauthorized presenter. While Proof-Of-Possession Semantics for JSON Web Tokens (JWTs) [POPS] touches briefly on the Sender Constraint, it is only one paragraph within a introductory text and does not discuss it in detail. Instead, it devotes much of the discussion to the Key Confirmation method. It also is making the usage of such token against the resource out of scope.

This discussion draft describes a way to express the Sender Constraint in the JWT, as well as one possible way of using it to access a protected resource.

1.1. Notational Conventions

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

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

2. Terminology

For the purpose of this document, the terms defined in RFC6749 [RFC6749] is used. In addition, following term is defined.

Authorized Presenter
Party that the token is intended to be used by.

3. Sender Constraint Representation

Sender Constraint is expressed by including the following member at the top level of JWT payload.

The Client ID of the Authorized Presenter.

Follwoing is an example of such JWT payload.

      "iss": "https://server.example.com",
      "sub": "joe@example.com",
      "azp": "clientID-1342050",
      "aud": "https://client.example.org",
      "exp": "1361398824",
      "nbf": "1360189224",

Figure 3-1 Example of Sender Constrained JWT.

4. Client Authentication

The resource that supports this specification MUST authenticate the Client. In this document a possible method is proposed as follows:

1. The authorized presenter issues a HEAD or GET request to the resource.

GET /resource/1234 HTTP/1.0
Host: server.example.com

2. The resource returns a HTTP 401 response with WWW-Authenticate header with "Named" scheme, whcih includes nonce.

HTTP/1.0 401 Unauthorized
Server: HTTPd/0.9
Date: Wed, 14 March 2015 09:26:53 GMT
WWW-Authenticate: Named nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093"

3. The client creates JWS compact seriarization over the nonce.

4. The client sends the request to the resource, this time with Authorize: header with Named scheme and access token and the JWS.

GET /resource/1234 HTTP/1.0
Host: server.example.com
Authorization: Named at="access.token.jwt", s="jws.of.nonce"

5. The resource server finds the client key corresponding to the value of azp in the access token. It may have been obtained through client registration at the Issuer.

6. The resource server creates the JWS of the nonce and compare it with the value of s of the Authorization header. If it fails, the process stops here and the resource access MUST be denied.

7. The resource server MUST verify the access token. If it is valid, the resource SHOULD be returned as HTTP resonse.

5. IANA Considerations

5.1. JSON Web Token Claim Registration

This specification registers the Destination Claim defined herein in the IANA JSON Web Token Claims registry defined in [I-D.ietf-oauth-json-web-token].

5.2. Registry Request Contents

6. Security Considerations

Needless to say, the client's secret key must be kept securely.

7. Acknowledgements


8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC 6749, October 2012.

8.2. Informative References

[POPA] Hunt, P., "OAuth 2.0 Proof-of-Possession (PoP) Security Architecture", March 2015.
[POPS] Jones, M., "Proof-Of-Possession Semantics for JSON Web Tokens (JWTs)", March 2015.

Appendix A. Document History

Removed most of the duplication with [POPS]
Included key confirmation method etc. The first version on the tools.ietf.org. (Prevous versions were sent just as email attachements.)

Author's Address

Nat Sakimura Nomura Research Institute EMail: sakimura@gmail.com