Custom authentication with Firebase

Hello everybody,

I want to make a mobile application in Unity using Firebase. Instead of email/password login I want to make nickname/password authentication (e.g. custom auth). Could somebody please explain to me (in a short way) what do I need to do? Like, do I need my own server? If yes, what should it do?

I’ve been searching before, but all I can find is authentication with email/phone number/google account and so on…

Thank you a lot!

Could somebody help me pls?