[OAUTH-WG] Use cases for Audience Restricted tokens + AS and RS "discovery"

[George Fletcher <[e-mail]>]

Goals:

1. Help the client not send a token to the "wrong" endpoint
    a. wrong AS /token endpoint
    b. evil RS endpoint(s)
2. Allow good RS to determine if the token being validated was intended 
for that RS

Other high-level goals?

Use cases:

1. RS that supports multiple AS (we've had this in production since 2011)
2. RS rejects token not issued for use at the RS
3. Client that dynamically supports new RS (say any client that supports 
the jabber API)
4. Client that dynamically supports new AS

Feel free to add to the list :)