Firebase Authentication in Flutter

Introduction

Firebase Authentication helps you easily add user sign-in to your app. It keeps user info safe and lets users log in quickly.

When you want users to create accounts and log in to your app.

When you need to protect parts of your app so only signed-in users can access them.

When you want to let users sign in with email/password or social accounts like Google.

When you want to manage user sessions without building your own backend.

When you want to quickly add secure authentication without much code.

Syntax

Flutter

final FirebaseAuth auth = FirebaseAuth.instance;

// Sign up with email and password
UserCredential userCredential = await auth.createUserWithEmailAndPassword(
  email: '[e-mail]',
  password: 'password123',
);

// Sign in with email and password
UserCredential userCredential2 = await auth.signInWithEmailAndPassword(
  email: '[e-mail]',
  password: 'password123',
);

// Sign out
await auth.signOut();

Use FirebaseAuth.instance to access authentication methods.

All sign-in and sign-up methods return a UserCredential object with user info.

Examples

This creates a new user account with email and password.

Flutter

final auth = FirebaseAuth.instance;

// Sign up new user
await auth.createUserWithEmailAndPassword(
  email: '[e-mail]',
  password: 'mypassword',
);

This signs in a user who already has an account.

Flutter

final auth = FirebaseAuth.instance;

// Sign in existing user
await auth.signInWithEmailAndPassword(
  email: '[e-mail]',
  password: 'mypassword',
);

This logs out the current user from the app.

Flutter

final auth = FirebaseAuth.instance;

// Sign out current user
await auth.signOut();

Sample App

This app lets users sign up, sign in, and sign out using Firebase Authentication with email and password. It shows messages for success or failure.

Flutter

import 'package:flutter/material.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:firebase_auth/firebase_auth.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: AuthExample(),
    );
  }
}

class AuthExample extends StatefulWidget {
  @override
  _AuthExampleState createState() => _AuthExampleState();
}

class _AuthExampleState extends State<AuthExample> {
  final FirebaseAuth _auth = FirebaseAuth.instance;
  final TextEditingController _emailController = TextEditingController();
  final TextEditingController _passwordController = TextEditingController();
  String _message = '';

  Future<void> _signUp() async {
    try {
      await _auth.createUserWithEmailAndPassword(
        email: _emailController.text.trim(),
        password: _passwordController.text.trim(),
      );
      setState(() {
        _message = 'Sign up successful!';
      });
    } catch (e) {
      setState(() {
        _message = 'Sign up failed: $e';
      });
    }
  }

  Future<void> _signIn() async {
    try {
      await _auth.signInWithEmailAndPassword(
        email: _emailController.text.trim(),
        password: _passwordController.text.trim(),
      );
      setState(() {
        _message = 'Sign in successful!';
      });
    } catch (e) {
      setState(() {
        _message = 'Sign in failed: $e';
      });
    }
  }

  Future<void> _signOut() async {
    await _auth.signOut();
    setState(() {
      _message = 'Signed out';
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Firebase Auth Example')),
      body: Padding(
        padding: EdgeInsets.all(16),
        child: Column(
          children: [
            TextField(
              controller: _emailController,
              decoration: InputDecoration(labelText: 'Email'),
              keyboardType: TextInputType.emailAddress,
            ),
            TextField(
              controller: _passwordController,
              decoration: InputDecoration(labelText: 'Password'),
              obscureText: true,
            ),
            SizedBox(height: 20),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceAround,
              children: [
                ElevatedButton(onPressed: _signUp, child: Text('Sign Up')),
                ElevatedButton(onPressed: _signIn, child: Text('Sign In')),
                ElevatedButton(onPressed: _signOut, child: Text('Sign Out')),
              ],
            ),
            SizedBox(height: 20),
            Text(_message, style: TextStyle(color: Colors.blue)),
          ],
        ),
      ),
    );
  }
}

Important Notes

Always initialize Firebase before using authentication.

Use try-catch to handle errors like wrong password or user not found.

Keep user passwords safe by never storing them yourself; Firebase handles this securely.

Summary

Firebase Authentication makes adding user login easy and secure.

Use createUserWithEmailAndPassword to sign up and signInWithEmailAndPassword to log in.

Always handle errors and show clear messages to users.