IMO, I'd use only firebase auth and chat personally. Firebase auth is supremely easy to implement, and you can write your own backend services (in node, rails,

IMO, I'd use only firebase auth and chat personally. Firebase auth is supremely easy to implement, and you can write your own backend services (in node, rails, Go, whatever) and auth your clients against it using the firebase sdk. Chat makes it supremely easy as well for simpler use cases, and if you do find it limiting, you can always swap it out for something better suited. In my case, I use firebase client sdk on mobile (react-native) and web (react). My backend (go + node) services use firebase admin sdk to authenticate requests, and my database is postgres.