Kotlin FirebaseAuth Login Issue: Debugging Guide

Firebase Authentication is a powerful tool for managing users in Android apps using Kotlin. However, developers often face login issues when using FirebaseAuth — especially when debugging email/password authentication. In this guide, we will walk through how to solve the FirebaseAuth not logging in problem in Kotlin.

Common Causes FirebaseAuth Fails to Log In:

• Invalid or null email/password inputs
• FirebaseAuth not properly initialized
• Wrong rules in Firebase console
• Email not verified
• No internet connection

We will debug step-by-step with full source code examples split by class to make your app authentication work correctly.

1. Gradle Setup

Ensure your dependencies are correctly set:

// app/build.gradle
implementation("com.google.firebase:firebase-auth-ktx:22.1.1")

Don’t forget to initialize Firebase in your Application class.

2. FirebaseAuthHelper.kt – Auth Utility Class

object FirebaseAuthHelper {
    private val auth: FirebaseAuth = FirebaseAuth.getInstance()

    fun loginUser(email: String, password: String, onSuccess: () -> Unit, onError: (String) -> Unit) {
        if (email.isBlank() || password.isBlank()) {
            onError("Email or Password must not be empty")
            return
        }

        auth.signInWithEmailAndPassword(email, password)
            .addOnCompleteListener { task ->
                if (task.isSuccessful) {
                    val user = auth.currentUser
                    if (user?.isEmailVerified == true) {
                        onSuccess()
                    } else {
                        onError("Email not verified")
                    }
                } else {
                    onError(task.exception?.localizedMessage ?: "Login failed")
                }
            }
    }
}

3. LoginActivity.kt – UI Logic

class LoginActivity : AppCompatActivity() {
    private lateinit var emailInput: EditText
    private lateinit var passwordInput: EditText
    private lateinit var loginButton: Button

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_login)

        emailInput = findViewById(R.id.emailEditText)
        passwordInput = findViewById(R.id.passwordEditText)
        loginButton = findViewById(R.id.loginButton)

        loginButton.setOnClickListener {
            val email = emailInput.text.toString().trim()
            val password = passwordInput.text.toString().trim()

            FirebaseAuthHelper.loginUser(email, password,
                onSuccess = {
                    Toast.makeText(this, "Login Success", Toast.LENGTH_SHORT).show()
                    startActivity(Intent(this, MainActivity::class.java))
                    finish()
                },
                onError = { message ->
                    Toast.makeText(this, message, Toast.LENGTH_LONG).show()
                }
            )
        }
    }
}

4. Firebase Console Check

Go to your Firebase Console > Authentication > Sign-in Method

• Make sure Email/Password is enabled
• Check Authentication Rules under Firestore or Realtime DB
• Ensure that user email is verified if required