Chore: Cleanup namespace and ID resolution (#79360)

* Chore: Cleanup namespace ID resolution

* Check for negative userID when relevant

* Reuse existing function for parsing ID as int

* Fix imports

pkg/services/authn/authnimpl/sync/oauth_token_sync.go

@@ -40,7 +40,7 @@ type OAuthTokenSync struct {
 }
 
 func (s *OAuthTokenSync) SyncOauthTokenHook(ctx context.Context, identity *authn.Identity, _ *authn.Request) error {
-	namespace, _ := identity.NamespacedID()
+	namespace, _ := identity.GetNamespacedID()
 	// only perform oauth token check if identity is a user
 	if namespace != authn.NamespaceUser {
 		return nil