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How to build a custom Facebook login button using Firebase Auth in Jetpack Compose

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This tutorial showcases how to create your own log in button to sign in with Facebook using Jetpack Compose and Firebase Authentication.

The Facebook SDK provides a standard Login Button view which you can use using the AndroidView composable. If you are looking for a way to implement a custom design and login flow in your app, keep reading.

Featured in Android Weekly #556

Add Facebook and Firebase to your Android project

We are going to use 3 different dependencies for this:

  • The Facebook SDK so that we launch the Facebook Log In flow.
  • Firebase Authentication so that we can forward the session to Firebase and see our signed in users in the Firebase console.
  • Jetbrain's kotlinx-coroutines-play-services so that we can wait for Firebase Tasks to complete without requiring an Activity.

Add the Play Services gradle plugin

In your /build.gradle file, include the Play Services dependencies in your buildscript:

buildscript {
    dependencies {
        // other dependencies

        classpath 'com.google.gms:google-services:4.3.15'
    }
}

In your app/build.gradle file, make use of the plugin:

plugins {
    // your other plugins
    id 'com.android.application'
    id 'org.jetbrains.kotlin.android'

    // this is the new one
    id 'com.google.gms.google-services'
}

Make sure to include your google-services.json file in your /app module folder:

Download google-services.json. Switch to the Project view in Android Studio to see your project root directory. Move the google-services.json into your Android app module root directory.

Include your apps SHA certificate fingerprints in the Firebase Console

It is important to include your application's SHA certificate fingerprints in your Firebase Project, otherwise the sign in will always fail.

If you are releasing your app to the Google Play Store you will need to generate and publish an App Bundle. As Google is the one singing your app via the Google Play Store, you can find the keys in the Google Play Store console.

However, if you are generating an APK, you can find the keys on your local machine.

Where to find the SHA key for your an App Bundle

Open the Google Play Console and select the app you want to add sign in to.

From the left side menu Go to Release -> Setup -> App Integrity

Where to find the app integrity option in the Google Console

Click on the 'App Signin' tab and copy the SHA1 value and paste it in your Firebase project's project settings.

Where to find the SHA key for your APK

Go to your project's terminal in Android Studio (or navigate to your project's root directory via your favorite terminal) and type ./gradlew signingreport

The command will print the SHA certificate fingerprints of different build variants of your project.

Copy the SHA1 value of the debug variant

./gradlew singing report

and paste them in your Firebase project's project settings.

Firebase SSH Fingerprints

if you are releasing the app to the Play Store, do the same for the release variant.

Include the Gradle dependencies

In your app/build.gradle file, add the following dependencies:

implementation platform('com.google.firebase:firebase-bom:31.1.1')
implementation 'com.google.firebase:firebase-auth-ktx'

implementation 'com.facebook.android:facebook-android-sdk:14.1.0'

implementation('org.jetbrains.kotlinx:kotlinx-coroutines-play-services:1.6.4')

Enable Facebook Sign-In via the Firebase Console

We need to tell Firebase that our app supports Facebook sign in. We could use Facebook alone to sign-in but we woud need a way to keep track of signed-in sessions. Firebase Authentication is used to do that heavy work for us.

In order to enable Facebook as a sign-in method in Firebase, you need some credentials from the Facebook Developer portal. This is not covered in this tutorial, but you can click here to watch how to enable Facebook Sign-In on Firebase.

By the end of the setup you should have

PS: The above is not an ordered list.

Build the custom login button with Facebook sign in flow

Let's build a composable that launches the Facebook sign-in flow once clicked.

The Facebook SDK provides an ActivityResultContract which we can use to launch the sign in flow. In order to create the contract, we need an instance of the LoginManager and optionally a CallbackManager. The CallbackManager will provide us the login callback and notify us for any successful events or failures.

Once we receive the result, we will forward it to Firebase Auth:

@Composable
fun FacebookButton(
    onAuthComplete: () -> Unit,
    onAuthError: (Exception) -> Unit,
    modifier: Modifier = Modifier,
) {
    val scope = rememberCoroutineScope()
    val loginManager = LoginManager.getInstance()
    val callbackManager = remember { CallbackManager.Factory.create() }
    val launcher = rememberLauncherForActivityResult(
        loginManager.createLogInActivityResultContract(callbackManager, null)) {
        // nothing to do. handled in FacebookCallback
    }

    DisposableEffect(Unit) {
        loginManager.registerCallback(callbackManager, object : FacebookCallback<LoginResult> {
            override fun onCancel() {
                // do nothing
            }

            override fun onError(error: FacebookException) {
                onAuthError(error)
            }

            override fun onSuccess(result: LoginResult) {
                // user signed in successfully
                // TODO Forward to Firebase Auth
                // check next step in composables.com/blog/firebase-auth-facebook
            }
        })

        onDispose {
            loginManager.unregisterCallback(callbackManager)
        }
    }
    Button(
        modifier = modifier,
        onClick = {
            // start the sign-in flow
            launcher.launch(listOf("email", "public_profile"))
        }) {
        Text("Continue with Facebook")
    }
}

What is left now is to wire the successful sign in to Firebase Auth.

loginManager.registerCallback(callbackManager, object : FacebookCallback<LoginResult> {

        // ....

        override fun onSuccess(result: LoginResult) {
            scope.launch {
                val token = result.accessToken.token
                val credential = FacebookAuthProvider.getCredential(token)
                val authResult = Firebase.auth.signInWithCredential(credential).await()
                if (authResult.user != null) {
                    onAuthComplete()
                } else {
                    onAuthError(IllegalStateException("Unable to sign in with Facebook"))
                }
            }
        }
}

Copy-pastable code to drop to your project

@Composable
fun FacebookButton(
    onAuthComplete: () -> Unit,
    onAuthError: (Exception) -> Unit,
    modifier: Modifier = Modifier,
) {
    val scope = rememberCoroutineScope()
    val loginManager = LoginManager.getInstance()
    val callbackManager = remember { CallbackManager.Factory.create() }
    val launcher = rememberLauncherForActivityResult(
        loginManager.createLogInActivityResultContract(callbackManager, null)) {
        // nothing to do. handled in FacebookCallback
    }

    DisposableEffect(Unit) {
        loginManager.registerCallback(callbackManager, object : FacebookCallback<LoginResult> {
            override fun onCancel() {
                // do nothing
            }

            override fun onError(error: FacebookException) {
                onAuthError(error)
            }

            override fun onSuccess(result: LoginResult) {
                scope.launch {
                    val token = result.accessToken.token
                    val credential = FacebookAuthProvider.getCredential(token)
                    val authResult = Firebase.auth.signInWithCredential(credential).await()
                    if (authResult.user != null) {
                        onAuthComplete()
                    } else {
                        onAuthError(IllegalStateException("Unable to sign in with Facebook"))
                    }
                }
            }
        })

        onDispose {
            loginManager.unregisterCallback(callbackManager)
        }
    }
    Button(
        modifier = modifier,
        onClick = {
            // start the sign-in flow
            launcher.launch(listOf("email", "public_profile"))
        }) {
        Text("Continue with Facebook")
    }

In this article you learnt how to build a custom Login Facebook button using Firebase Authentication and Jetpack Compose. We added the required dependencies and used the LoginManager.createLogInActivityResultContract() to launch the login flow when our Button is clicked.

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