+There is one special exception to the scope rules: a valid token is always allowed to issue a request to "@GET /arvados/v1/api_client_authorizations/current@":{{ site.baseurl }}/api/methods/api_client_authorizations.html#current regardless of its scopes. This allows clients to reliably determine whether a request failed because a token is invalid, or because the token is not permitted to perform a particular request. The API server itself needs to be able to do this to validate tokens issued by other clusters in a federation.
+