OAuth: Use the attached external session data in OAuthToken and OAuthTokenSync (#96655)

* wip

* wip + tests

* wip

* wip opt2

* Use authn.Identity struct's SessionToken

* Merge fixes

* Handle disabling the feature flag correctly

* Fix test

* Cleanup

* Remove HasOAuthEntry from the OAuthTokenService interface

* Remove unused function

pkg/services/authn/authnimpl/service.go

@@ -322,7 +322,7 @@ func (s *Service) Logout(ctx context.Context, user identity.Requester, sessionTo
 			goto Default
 		}
 
-		clientRedirect, ok := logoutClient.Logout(ctx, user)
+		clientRedirect, ok := logoutClient.Logout(ctx, user, sessionToken)
 		if !ok {
 			goto Default
 		}