Soft-warn about application default credentials using gcloud credentials #198
Description
Due to user issues with quota and API enablement, the auth libraries should issue a soft warning (that can be silenced) when application default credentials uses user credentials from the Cloud SDK. They should not warn if the credentials for the cloud sdk are service account credentials.
Your application has authenticated using end user credentials from Google
Cloud SDK. We recommend that most server applications use service accounts
instead. If your application continues to use end user credentials from Cloud
SDK, you might receive a "quota exceeded" or "API not enabled" error. For
more information about service accounts, see
https://cloud.google.com/docs/authentication/.
Additional context:
https://groups.google.com/a/google.com/forum/#!topic/client-auth-team/DKqrFw6lL1Q
https://buganizer.corp.google.com/issues/64388723
googleapis/google-auth-library-python#266