Adds an MVC interceptor for relaying OAuth2 access tokens into the client context (if
there is one). In this way an incoming request to a resource server can be relayed
downstream just be using
@EnableOAuth2Client and an
OAuth2RestTemplate. An MVC interceptor is used so as to have a minimal
impact on the call stack. If you are not using MVC you could use a custom filter or AOP
interceptor wrapping the same call to an
AccessTokenContextRelay.
N.B. an app that is using
UserInfoTokenServices generally doesn't need this
interceptor, but it doesn't hurt to include it.