I would like to use Firebase Auth to authenticate mobile phone clients, but I have an existing PostgreSQL database with lots of functions and triggers that I do not want to convert to NoSQL. Is it possible to authenticate users with Firebase and then allow them to read and write data to the PostgreSQL database securely? What would be the proper way to do this? I come from a web development background so I'm used to session-based authentication instead of token-based authentication. Trying to wrap my head around it.
If you already have a backend talking to your PostgreSQL database, you can get a token with user.getToken() (https://firebase.google.com/docs/reference/android/com/google/firebase/auth/FirebaseUser#public-constructor-summary) and then verify the token on your backend (https://firebase.google.com/docs/auth/admin#id_token_verification). Then, use the uid from the token as the user's ID.