Extract preferred_username_claims also from the id_token if present

[MarcialRosales]

Is your feature request related to a problem? Please describe.

RabbitMQ always extracts the user identity from a number of claim found in the access_token itself. The access_token is one of the attributes of a successful Access Token Response.

According to the OAuth2 spec, a successful Access Token Response should have, at least, an access_token attribute in addition to others such as expires_in. However, some OAuth Providers (like Auth0) may include an id_token to a successful Access Token Response. The id_token contains user’s authentication information such as username, user_ids, and others. When this happens, the access_token only contains the sub claim which commonly refers to an internal user identifier which the user cannot relate to.

Describe the solution you'd like

RabbitMQ should look up auth_oauth2.preferred_username_claims in the access_token and also in the id_token if present in the Access Token Response.

Describe alternatives you've considered

No response

Additional context

No response