10.2 Authentication

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10.2 Authentication

Firebase Authentication provides backend services, easy-to-use SDKs, and ready-made UI libraries to authenticate users to your app. It supports authentication using passwords, phone numbers, popular federated identity providers like Google, Facebook and Twitter, and more

Setting up Authentication

Make sure your Firebase project is set up, the steps of which are covered in the first section 11.1!

Add these two dependencies to your module-level Gradle file:

implementation 'com.google.firebase:firebase-auth-ktx'
implementation 'com.google.android.gms:play-services-auth:19.0.0'

These dependencies add the Firebase Authentication Android library and Google Play services SDK to your app.

When accessing most Authentication services, you need the appropriate FirebaseAuth object.

First, declare your auth variable:

private lateinit var auth: FirebaseAuth

In the onCreate/onCreateView method of your activity/fragment, initialize the auth variable as so:

auth = Firebase.auth

General

Check for signed-in users

When initializing your Activity, check to see if the user is currently signed in in your onStart method (which is called automatically after onCreate):

override fun onStart() {
    super.onStart()
    val currentUser = auth.currentUser
    if (currentUser == null) {
        /**
         * No user is currently signed in, can update UI elements to account for this
         * or maybe redirect to some sign in activity!
         */
    } else {
        /**
         * A signed in user is detected, carry out some respective actions if needed!
         */
    }
}

Sign-out

You can sign out a user using:

Firebase.auth.signOut()

This will most likely just be a collection of the links below, some personal reflections also!

private lateinit var googleSignInClient: GoogleSignInClient

......

// Configure sign-in to request the user's ID, email address, and basic
// profile. ID and basic profile are included in DEFAULT_SIGN_IN.
val gso = GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
        .requestIdToken(getString(R.string.default_web_client_id))
        .requestEmail()
        .build()

googleSignInClient = GoogleSignIn.getClient(this, gso)

3. Add an ActivityResultLauncher for the Google Sign In Activity intent (the API launches a separate activity to sign the user in):

    private lateinit var intentLauncher: ActivityResultLauncher<Intent>
    override fun onCreate(savedInstanceState: Bundle?) {
        ...
        intentLauncher =
            registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
                ...
            }
        ...
    }

4. You can add a handy Google sign-in button via:

<com.google.android.gms.common.SignInButton
 android:id="@+id/sign_in_button"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content" />
 
 <!--  Can add app:buttonSize attribute and specifiy icon_only, standard, or wide-->
 <!--  Can add app:colorScheme attribute and specifiy dark, light, or auto-->

5. You can then register the OnClickListener for this button in your activity via:

findViewById<SignInButton>(R.id.sign_in_button).setOnClickListener(this)

override fun onClick(view: View?) {
    if (view != null) {
        when (view.id) {
            R.id.sign_in_button -> {
                signInGoogle();
            }
        // ...
        }
    }
}

private fun signInGoogle() {
    val signInIntent = googleSignInClient.signInIntent
    intentLauncher.launch(signInIntent)
}

7. Expand the intent launcher

private lateinit var intentLauncher: ActivityResultLauncher<Intent>
override fun onCreate(savedInstanceState: Bundle?) {
    ...
    intentLauncher =
        registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
            if (result.resultCode == Activity.RESULT_OK) {
                val task = GoogleSignIn.getSignedInAccountFromIntent(result.data)
                try {
                    // Google Sign In was successful, authenticate with Firebase
                    val account = task.getResult(ApiException::class.java)!!
                    firebaseAuthWithGoogle(account.idToken!!)
                } catch (e: ApiException) {
                    // Google Sign In failed, update UI appropriately
                }
            }
        }
    ...
}

8. After a user successfully signs in, get an ID token from the GoogleSignInAccount object, exchange it for a Firebase credential, and authenticate with Firebase using the Firebase credential:

    private fun firebaseAuthWithGoogle(idToken: String) {
        val credential = GoogleAuthProvider.getCredential(idToken, null)
        auth.signInWithCredential(credential)
            .addOnCompleteListener(this) { task ->
                if (task.isSuccessful) {
                    /**
                     * A signed in user is detected, carry out some respective actions if needed!
                     */
                    val user = auth.currentUser
                    ...
                } else {
                    /**
                     * No user is currently signed in, can update UI elements to account for this
                     * and display some feedback to the user.
                     */
                }
            }
    }

9. All done :)

Password Authentication

2. When a new user signs up using your app's sign-up form, complete any new account validation steps that your app requires, such as verifying that the new account's password was correctly typed and meets your complexity requirements.

EditTexts are very useful for fields for input for emails/passwords!

3. Create a new account by passing the new user's email address and password to createUserWithEmailAndPassword:

auth.createUserWithEmailAndPassword(email, password)
        .addOnCompleteListener(this) { task ->
            if (task.isSuccessful) {
                /**
                 * A signed in user is detected, carry out some respective actions if needed!
                 */
                val user = auth.currentUser
            } else {
                /**
                 * No user is currently signed in, can update UI elements to account for this
                 * and display some feedback to the user.
                 */
            }
        }

Creating an account automatically signs a user in!

If given some email and password, you can sign in a user with signInWithEmailAndPassword:

auth.signInWithEmailAndPassword(email, password)
        .addOnCompleteListener(this) { task ->
            if (task.isSuccessful) {
                /**
                 * A signed in user is detected, carry out some respective actions if needed!
                 */
                val user = auth.currentUser
                ...
             } else {
                /**
                 * No user is currently signed in, can update UI elements to account for this
                 * and display some feedback to the user.
                 */
            }
        }