auth_util.GetUserEmail
If we don't support client id, then:
* For UI endpoints, always use cookie-based auth without checking client ids.
* For API endpoints:
- For service accounts, always use oauth-based auth to check emails
- For admins to test, always use oauth-based auth to check both emails and Cloud Endpoint client id
Comment 1 by st...@chromium.org
, Aug 21 2017