I was looking for a reliable authentication system for my backend, my current API implementation is in PHP and MySQL. I would like to integrate what Google Identity Toolkit promises, but now there is a strong suggestion by them to use Firebase Authentication. Can I use Firebase authentication without using Firebase for the data storage, so keeping my MySQL DB structure for the data storage and Firebase for the Auth? Is there any performance issue?
you can use this scheme apparently there is no issue, since you will be doing this with firebase as well (authenticating user and then storing data in firebaseDB). but the flexibility of easily controlling the access on database with firebase rules will be missing in your scenario. You have to then implement the access control on your database separately