The platform base URL.
An auth provider for the request.
The attribute value FQN to check.
true if the value exists, false if it does not.
ConfigurationError if the FQN format is invalid or the URL is insecure.
NetworkError if a service error occurs.
Reports whether the attribute value FQN exists on the platform.
valueFqnshould be a full attribute value FQN (with/value/segment):https://<namespace>/attr/<attribute_name>/value/<value>