To add something more on this. 'googleusercontent.com' domain is used for any customer originated traffic from within the Google Infrastructure. This includes both Google App Engine and Google Compute Engine.
In addition to what Barry said, if the requests were made by URLFetch, there should be an "X-Appengine-Inbound-Appid" header [1] <https://cloud.google.com/appengine/docs/python/appidentity/#Python_Asserting_identity_to_other_App_Engine_apps> that identifies the requesting GAE App. [1] https://cloud.google.com/appengine/docs/python/appidentity/#Python_Asserting_identity_to_other_App_Engine_apps -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/google-appengine. To view this discussion on the web visit https://groups.google.com/d/msgid/google-appengine/3c8b0fb7-b3b0-42dc-ac8d-2ebf01720d96%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
