A complete login example using a Fusion Table (obsolete) as simple as possible - Taifun
Login Using FireBase DB - TimAI2
Register and Login using Firebase Authentication for your app - TimAI2
Login with Google Oauth - Diego Barreiro
Login with TinyDB, single user - ABG
How to Make A ‘Remember Me’ checkbox - Alpha2020
Login/Register using Google Sheets & simpleCrypto - TimAI2