How to Implement Firebase Authentication API in Kotlin

Set Up Firebase Authentication in Your Project

• Include the Firebase SDK in your `build.gradle` file (app level). Ensure you have the necessary Firebase dependencies:

dependencies {
    implementation platform('com.google.firebase:firebase-bom:32.0.0')
    implementation 'com.google.firebase:firebase-auth-ktx'
    // Add other Firebase products as needed
}

Initialize Firebase Authentication

• Initialize Firebase in your application class or main activity:

class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()
        FirebaseApp.initializeApp(this)
    }
}

Create an Instance of FirebaseAuth

• In your activity or fragment, create an instance of `FirebaseAuth` to handle authentication operations:

private lateinit var auth: FirebaseAuth

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    
    auth = FirebaseAuth.getInstance()
}

Register New Users

• To enable user signup, use `createUserWithEmailAndPassword`. This function requires an email and a password:

fun registerUser(email: String, password: String) {
    auth.createUserWithEmailAndPassword(email, password)
        .addOnCompleteListener(this) { task ->
            if (task.isSuccessful) {
                val user = auth.currentUser
                // Handle registered user
            } else {
                // Handle error
            }
        }
}

Sign In Users

• To sign in users, use `signInWithEmailAndPassword`. This will authenticate existing users with their credentials:

fun loginUser(email: String, password: String) {
    auth.signInWithEmailAndPassword(email, password)
        .addOnCompleteListener(this) { task ->
            if (task.isSuccessful) {
                val user = auth.currentUser
                // Handle signed in user
            } else {
                // Handle error
            }
        }
}

Verify Email

• To verify email addresses, send a verification email after registration:

fun sendEmailVerification() {
    val user = auth.currentUser
    user?.sendEmailVerification()
        ?.addOnCompleteListener { task ->
            if (task.isSuccessful) {
                // Email sent
            } else {
                // Error occurred
            }
        }
}

Reset Password

• Allow users to reset their passwords by sending a password reset email:

fun sendPasswordReset(email: String) {
    auth.sendPasswordResetEmail(email)
        .addOnCompleteListener { task ->
            if (task.isSuccessful) {
                // Email sent
            } else {
                // Error occurred
            }
        }
}

Sign Out Users

• To sign a user out, call `signOut()` from your `FirebaseAuth` instance:

fun signOutUser() {
    auth.signOut()
    // User is signed out
}

Handle User State Changes

• Monitor user's authentication state across the app:

override fun onStart() {
    super.onStart()
    val currentUser = auth.currentUser
    updateUI(currentUser)
}

private fun updateUI(user: FirebaseUser?) {
    // Update UI based on user's authentication state
}

Manage Anonymous Authentication

• Enable anonymous authentication by signing in users anonymously:

fun signInAnonymously() {
    auth.signInAnonymously()
        .addOnCompleteListener(this) { task ->
            if (task.isSuccessful) {
                val user = auth.currentUser
                // Handle signed-in anonymously user
            } else {
                // Handle error
            }
        }
}