I have a question, let's say I have a website and app both using oAuth facebook login. Should I save the access token provided by facebook in my database and if I should, what will happen to the access token when user logins with facebook on website and then login again with the app? is that mean access token is going to be overwritten by new login? and do you have any other suggestions for 0auth integration?

Dropping this here to get updates
I'd like to know too

@Froot seems like no one wants to help us :/

This is general to OAuth, should apply to Facebook as well. Save the access token if you need offline access to whatever scope you requested. Use the token to retrieve the user's unique ID and save that as the user's identifier in your database.

Next time when they login on any channel (web, app, etc.), use the token received to access the user ID again. Look it up in your database and you'll be able to establish who it is.