I am using GAE’s Python environment and Janrain in order to provide multiple ways to login in my service.
Based on login information I receive from Janrain, I create a google.appengine.api.User object and store it to the datastore. Is there a way to handle this new object with the built-in get_current_user()? I need to be able to determine whether the requester is logged in or not and who the user is.
No, you cannot use your custom user objects with the native GAE Users API.
You could use a sessions library to track whether or not the request is coming from a logged in user (and who that user is). I recommend gae-sessions. The source includes a demo which shows how to integrate the sessions library with Janrain/RPX.
Disclaimer: I wrote gae-sessions, but for an informative comparison of it with alternatives, read this article.