When a client initially connects to Firebase, it is anonymous and is granted a default set of permissions as specified in your Security Rules. To grant a client a different set of permissions, you must authenticate it.
If you have your own server and like to control your own authentication, or you wish to integrate existing authentication mechanisms with Firebase; you can generate auth tokens yourself. See Custom Login for more details.
Firebase Simple Login
If you would like to use Firebase to manage your authentication, you can use the Firebase Simple Login service. The following authentication mechanisms are supported: