OAuth2AuthenticationToken.ClientRegistration -> AuthorizedClient #4520
Description
The OAuth2AuthenticationToken currently has a ClientRegistration attribute associated with it.
However, it makes much more sense to replace this and introduce a new construct that represents an instance of an Authorized Client.
An OAuth2AuthenticationToken represents a combination of an authentication of an end-user at the external identity provider as well as an authorized client by the end-user during the consent/authorization step of the Authorization Code grant flow. It makes a lot more sense to have an AuthorizedClient construct given that it's really an instance of ClientRegistration. For example, the same client (from a ClientRegistration) may be authorized more than once depending on the authorization grants it's configured with and the flows it's goes through.