On Google app engine web applications, what are the authentication options other than Google identity platforms?
Google AppEngine is a generic platform and you can implement any authentication option that supports web. For example Facebook Connect, Linked In, GitHub, etc.
Refer to a specific authentication platform documentation for implementation details.
Can a login/ authentication page for a Google app engine (python)  web application be created, without using the Google identity platform (but possibly a platform common for users having emails on other domains)?
Note: Other email address domains not other social media applications.