The platform base URL.
An auth provider for the request.
The attribute-level FQN to check.
true if the attribute exists, false if it does not.
ConfigurationError if the FQN format is invalid or the URL is insecure.
NetworkError if a non-not-found service error occurs.
Reports whether the attribute definition identified by
attributeFqnexists on the platform.attributeFqnshould be an attribute-level FQN (no/value/segment):https://<namespace>/attr/<attribute_name>