I have been pulling my hair out a few days on this issue, I have integrated facebook login on many other servers with no issues, but on appengine this is a major challenge. I have followed all of the steps to
enable curl and enable billing as outlined on the developer site, however despite this I still do not receive a facebook session after authentication and the page is redirected, there are many learning curves in app engine I understand but I cannot find much documentation for facebook login on appengine anywhere.