Authenticate with Firebase on Android Using a Custom Authentication System

You can integrate Firebase Authentication with a custom authentication system by modifying your authentication server to produce custom signed tokens when a user successfully signs in. Your app receives this token and uses it to authenticate with Firebase.

Before you begin

1. If you haven't already, add Firebase to your Android project .
2. In your module (app-level) Gradle file (usually <project>/<app-module>/build.gradle.kts or <project>/<app-module>/build.gradle ), add the dependency for the Firebase Authentication library for Android. We recommend using the Firebase Android BoM to control library versioning.

    dependencies 
     
    { 
     
     // Import the BoM 
   for the Firebase platform 
     
    implementation 
    ( 
    platform 
    ( 
    "com.google.firebase:firebase-bom:34.6.0" 
    )) 
     
     // Add the dependency for the Firebase Authentication 
   library 
     
    // When using the BoM 
   , you don't specify versions in Firebase library dependencies 
     
     implementation 
    ( 
    "com.google.firebase:firebase-auth" 
    ) 
    } 
   

   By using the Firebase Android BoM , your app will always use compatible versions of Firebase Android libraries.

   (Alternative)   Add Firebase library dependencies  without  using the BoM

   If you choose not to use the Firebase BoM , you must specify each Firebase library version in its dependency line.

   Note that if you use multiple Firebase libraries in your app, we strongly recommend using the BoM to manage library versions, which ensures that all versions are compatible.

    dependencies 
     
    { 
     
     // Add the dependency for the Firebase Authentication 
   library 
     
    // When NOT using the BoM 
   , you must specify versions in Firebase library dependencies 
     
     implementation 
    ( 
    "com.google.firebase:firebase-auth:24.0.1" 
    ) 
    } 
   

3. Get your project's server keys:
   1. Go to the Service Accounts page in your project's settings.
   2. Click Generate New Private Key at the bottom of the Firebase Admin SDK section of the Service Accounts page.
   3. The new service account's public/private key pair is automatically saved on your computer. Copy this file to your authentication server.

Authenticate with Firebase

1. In your sign-in activity's onCreate method, get the shared instance of the FirebaseAuth object:

   Kotlin

    private 
     
    lateinit 
     
    var 
     
    auth 
    : 
     
    FirebaseAuth 
    // ... 
    // Initialize Firebase Auth 
    auth 
     
    = 
     
    Firebase 
    . 
    auth 
    CustomAuthActivity 
    
    
    . 
    kt