[WG-UMA] Allow ID Tokens as RPT

Hi again, Another suggestion for consideration in UMA-next is whether we should support ID Tokens as an alternative to OAuth2 access tokens for bearer tokens from the Client to the RS. As the ID Token would be minted by the AS, then it should be able to introspect it just as it would an access token. This would also have an advantage in the token-first flow I outlined in my other mail, where the Client can use the additional claims part of requesting an ID Token in OpenID Connect to get the AS to eagerly get extra claims for the user, for example at the time of enrolment. Cheers James