What is this error: Authentication for the Google Apps domain undefined?

[Chris Xing]

I am trying to build a simple Google App engine app. Everything works on my dev machine. After deploying to App Engine, I am getting this error in log:

Thu May 05 22:22:25 UTC 2016 WARN Authentication for the Google Apps domain undefined can only be performed when requests are served from a subdomain of that domain or it has been approved through the Google Apps Control Panel. See https://developers.google.com/appengine/articles/auth

What does this error mean?

[Zeehad (Cloud Platform Support)]

Are you requiring user authentication for a Google Apps domain? From the settings page, check to see what Google Authentication is set to.

[Chris Xing]

Thanks! That was the problem.

On Fri, May 6, 2016 at 2:58 PM -0700, "'Zeehad (Cloud Platform Support)' via Google App Engine" <google-a...@googlegroups.com> wrote:

Are you requiring user authentication for a Google Apps domain? From the settings page, check to see what Google Authentication is set to.

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