Backend web service with Facebook login [duplicate]

Question

I'm creating a mobile app and a backend for it to talk to. I'm getting stuck on the registration and login.

If I have the user register via Facebook on the client, I'm storing their basic info and fb id. Should I be storing the access token I get back from Facebook?

And then, when I have a user login (already having an account on my backend), what should I be sending to the backend after the client logs in via Facebook? Being there's no password to send, I can't think of how the user can verify themselves to the backend.

Perhaps I'm just overlooking something, but any help is appreciated. For some context, the mobile app is iOS and the backend is being designed with Flask and MongoDB

Answer 1

Have a look at the following question/answers: Design for Facebook authentication in an iOS app that also accesses a secured web service

This should give you some ideas.