Mobile App Authentication in API?

Question

API

Tell me how it would be more correct to authenticate a mobile application in the API with which it works.
My task will be to write the API for this application. As a universal authentication method, we are looking at Firebase Authentication . Interested in how this triangle will interact.
Suppose a user downloads an application from the AppStore / PlayMarket, as I understand it, they issue some kind of UserID or DeviceID (I did not understand the mechanism until the end). Next, I need to register a user in the database, with the ability to link social networks and email to this account in the future.
Anyone with real experience please share.

Answer 1

You're right, it's a triangle. Firebase does not oblige you to use their database.
It is Orthodox to make a callback from Firebase to your server, but I did not see this in the documentation.
You need to send requests from the client to your server.
All user information can be viewed in the FIRUser object .
Several ways to enter: It's simple - the FIRUser object will not change. Associates login methods and Firebase user. You have delegated authentication.
Working with your database : use the ID as a binding parameter, no matter which way the user chooses to log in.