Provides a set of credentials that will always return an empty access token.
This is useful for APIs which do not require authentication, for local
service emulators, and for testing.
|public fetchAuthToken(?callable $httpHandler = NULL)|
Fetches the auth token. In this case it returns an empty string.
Returns the cache key. In this case it returns a null value, disabling
Fetches the last received token. In this case, it returns the same empty string