OAuth Working Group M. Kelly
Internet-Draft Stateless
Intended status: Standards Track N. Sakimura, Ed.
Expires: January 23, 2016 Nomura Research Institute
July 22, 2015

JSON Metadata for OAuth Responses 1.0


This specification defines an extensible metadata member that may be inserted into the OAuth 2.0 responses to assist the clients to process those responses. It is expressed as a member called "_links" that is inserted as the top level member in the responses. It will allow the client to learn where the members in the response could be used and how, etc. Since it is just a member, any client that does not understand this extension should not break and work normally while supporting clients can utilize the metadata to its advantage.

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Table of Contents

1. Introduction

Although OAuth 2.0 [RFC6749] has been known for its REST friendliness, OAuth itself is not RESTful, as it heavily relies on out-of-band information to drive the interactions. This situation can be eased by hypertext-enabling the JSON responses through the introduction of a member that represents such hypertext and other metadata. To achieve this, this specification introduces a top level member _links that represents various link relationships and other metadata.

2. Requirements

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].

3. JSON Meta Object

A JSON Meta Object uses the format described in [RFC4627] and is intended to be inserted into a JSON document to express some of the metadata associated with it as _links member.

The value of the _links member is a JSON object that expresses link relations (rel), which in turn holds an object with href and other members or an array of such objects.

Following non-normative schematic example should help envisage what it would look like. (Note: line-wraps are for display purpose only.)

              "Authorize":"{token_type} {access_token}"

Here, we have _links member that expresses various "relations" such as self and userinfo, which is a resource type of OpenID Connect's Userinfo endpoint. Each relationships has either a link relations object or an array of link relations objects as its value. The link relations objects holds various members such as href. They are explained in the next section.

3.1. _links Member

_links member holds exactly one object that contains the following members with relation as the string defined in [RFC4627]. The string SHOULD be a link relation type that is either defined in the IANA registry defined in Web Linking [RFC5988] or a URI that describes the relation.

Each relation member holds exactly one object or one array, whose elements are objects. Each object has following members, which are all optional.

3.1.1. href

The value of the href member is a URI Template [RFC6570] that the relation points to. The values for template parameters SHOULD be taken from the value of the top-level members in the including JSON object whose string matches the template variable name.

3.1.2. Authorize

The HTTP Authorize header defined in Hypertext Transfer Protocol -- HTTP/1.1 [RFC2616] to be used when accessing the resource identified by href. It is templated in exactly the same syntax as in URI Template [RFC6570] except that it is applied to the Authorization request header than the URI.

3.1.3. content-type

The content-type to be used when the parameters are sent to the URL.

[todo] Locate the proper reference and name for content transfer encodings.

e.g., application/x-www-form-urlencoded, multipart/form-data, application/json.

4. Application to the OAuth 2.0 Token Endpoint Responses

To create the Section 3 should be used in the token endpoint responses of the OAuth 2.0 Authorization Framework [RFC6749], following relations SHOULD be included.

4.1. Successful Responses

In the case of the Successful Response described in section 5.1. of [RFC6749], the following member SHOULD be present in the value of the _links member described in _links Member [_links] of this specification.

4.1.1. self

An object with the following members.

REQUIRED. The URI that resulted in this response.

4.1.2. describedby

An object with the following members.

REQUIRED. The value is one of the following URIs: http://tools.ietf.org/html/rfc6749#section-4.1.4 (Access Token Response of Authorization Code Grant), http://tools.ietf.org/html/rfc6749#section-4.3.3 (Access Token Response of Resource Owner Password Credentials Grant), http://tools.ietf.org/html/rfc6749#section-4.4.3 (Access Token Response of Client Credentials Grant ). [[editor's note. Add Assertion Flows as well.]]

4.1.3. Protected Resources

Each protected resources MUST provide a unique Relation Name by either registering to the Link Relation Type Registry defined in section 6.2 of [RFC5988]or providing an absolute URI that provides a collision registant name. The value is an array of objects that has the following members.

REQUIRED. The URI template that describes the request to the resource as described in href [href].
OPTIONAL. As described in content-type [ctype].
OPTIONAL. HTTP Authorization header to be sent when accessing the resource. This is described in Authorize [authz]. If this member is not available, then the client SHOULD access the expanded href value to obtain the Authorization header response to learn what authorization scheme it should use.

4.2. Error Responses

In the case of the Error Response described in section 5.2. of [RFC6749], the folloing member SHOULD be present.

4.2.1. self

An object with the following members.

REQUIRED. The URI that resulted in this response.

4.2.2. describedby

An object with the following members.

REQUIRED. The value is "http://tools.ietf.org/html/rfc6749#section-5.2".

5. IANA Considerations

5.1. Link Type Registration

Pursuant to [RFC5988], the following link type registrations [[will be]] registered by mail to link-relations@ietf.org.

5.1.1. OAuth 2 Registrations

The secition 3 of the OAuth 2.0 Authorization Framework [RFC6749] defines two endpoints that may be discovered through this specification. These are the user Authorization Endpoint and the Token Endpoint. Authorization Endpoint Token Endpoint

6. Security Considerations

6.1. href tampering

Unless integrity protected channel is used, an attacker may be able to tamper the value of the href thereby causing the receiver of the JSON response to send a request to the URL under the attacker's control with potentially confidential information contained in the parameters. To mitigate this risk, an integrity protected channel such as TLS protected channel should be used.

7. Acknowledgements

This specification borrows heavily from [HAL]. The Link type registration is taken from [oauth-lrdd].


8. Document History




9. References

9.1. 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.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, DOI 10.17487/RFC2616, June 1999.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, DOI 10.17487/RFC5988, October 2010.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M. and D. Orchard, "URI Template", RFC 6570, DOI 10.17487/RFC6570, March 2012.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC 6749, DOI 10.17487/RFC6749, October 2012.

9.2. Informational References

[HAL] Kelly, M., "JSON Hypermedia API Language", February 2013.
[oauth-lrdd] Mills, W., "Link Type Registrations for OAuth 2", October 2012.
[RFC4627] Crockford, D., "The application/json Media Type for JavaScript Object Notation (JSON)", RFC 4627, DOI 10.17487/RFC4627, July 2006.

Authors' Addresses

Mike Kelly Stateless EMail: mike@stateless.co
Nat Sakimura (editor) Nomura Research Institute EMail: sakimura@gmail.com