Yeah I don't mind setting up auth. It takes like a week at most for your MVP.
Firebase auth is as easy as it gets for auth. Want Username/Pass? Just enable it. Want Google, Twitter, Firebase, Apple, Github, etc.? Just enable it, and write the handlers.
Want to hook into your own SQL database? Easy. Set up a firebase listener, that handles the auth event, and write whatever you want (username, auth details) to SQL.
This is a 100% solved problem and Firebase does a superb job it it.