Modularizing Auth 2.0 Discovery

[Martin Atkins]

Recordon, David wrote:
> Well there already is the Yadis spec.  Maybe the Yadis spec remains
> separate versus becoming part of the OASIS XRI Resolution document?
> 

The XRDS-related parts of the Yadis specification seem to duplicate 
requirements from XRI Resolution chapter 3.

In the interests of avoiding redundancy, I'd suggest the following 
distinction:
  1. XRI Resolution chapter 3 (or a separate spin-off spec) describes 
the syntax of an XRDS document.
  2. Yadis describes how to obtain an XRDS document for an HTTP or HTTPS 
URL.
  3. OpenID Authentication describes how to determine the endpoint URI 
and other information from an XRDS document, referencing [1].
  4. The new HTTP discovery specification would reference [2] and [3] to 
describe the XRDS-based HTTP discovery mode, and then go on to describe 
the HTML-based discovery fallback.

Alternatively, [3] above could be served by a separate spec "OpenID 
discovery using XRDS", though I think that may be overkill for something 
so straightforward.