The OAuth working group has defined an authorization protocol [1] for 
delegating access to protected resources. Once access has been authorized, the 
client is issued a set of token credentials which are uses to make 
authenticated HTTP requests. To accomplish that, the OAuth working group has 
proposed two new HTTP authentication schemes: Bearer [2] and MAC [3].

The working group has been debating the issue of what's the best current 
practice for returning an error status in an HTTP authentication scheme. The 
Basic and Digest schemes do not specify the error condition and simply return a 
401 response with a new challenge. The MAC proposal follows this pattern.

The Bearer scheme proposal is taking a more active approach, defining an 
'error' response attribute for use with the WWW-Authenticate header and an 
error code registry to go along. The parameter and registry (especially the 
registry) are meant for reuse by other HTTP authentication schemes. At the 
moment, the three error conditions proposed by the Bearer draft are: invalid 
request, invalid token, and insufficient scope (which arguably is better suited 
using a 403 response with or without a new challenge).

While these error codes arguably do not provide an immediate actionable value 
(pending the help of future discovery specifications), the attribute and 
registry propose a forward-looking solution for when clients will be able to 
automatically resolve such issues (with the help of future discovery 
specifications).

The OAuth WG is seeking guidance on the following questions:

1. Should the WG define a general purpose method for returning errors with a 
401 WWW-Authenticate headers, including a cross-scheme error code registry?

If you answered yes to #1:

2. Should the WG apply this to all new HTTP authentication schemes (currently, 
MAC, but potentially more)?
3. Should this new error attribute and registry be part of the main OAuth 2.0 
specification, part of one of the upcoming schemes (for use with other 
schemes), or standalone?

If you answered no to #1:

4. Should the Bearer draft retain the attribute and registry for its own 
scheme-specific needs?

EHL

[1] http://tools.ietf.org/html/draft-ietf-oauth-v2-15
[2] http://tools.ietf.org/html/draft-ietf-oauth-v2-bearer-04
[3] http://tools.ietf.org/html/draft-hammer-oauth-v2-mac-token-03


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