Linking custom auth provider with Firebase

Linking Custom Auth Provider with Firebase

Firebase Authentication provides a robust platform for managing user authentication in web and mobile applications. While Firebase offers pre-built authentication providers like Google, Facebook, and email/password, you might need to integrate with your own custom authentication system for specific needs. This article will guide you through the process of linking a custom auth provider with Firebase.

Prerequisites

• Firebase Project: You need an existing Firebase project.
• Custom Authentication System: You should have a custom authentication system (e.g., your own backend server) ready to handle user authentication.

Steps to Link Custom Auth Provider

1. Configure Firebase

• Go to your Firebase console and navigate to the Authentication section.
• Under “Sign-in method,” click on “Add another sign-in method.”
• Select “Phone” as the sign-in method. (We will use phone authentication as an example, but you can adapt it to your custom auth system.)
• Enable Phone Authentication and configure the phone number settings.

2. Implement Custom Authentication Logic

The key to linking a custom auth provider is to implement your own authentication logic and integrate it with Firebase. Here’s a basic outline:

A. User Sign-Up

• Your server should receive sign-up requests with the user’s credentials.
• Validate the user’s information (e.g., check for existing accounts, enforce password complexity).
• If the validation is successful, create a new user record on your server.
• Generate a custom token that identifies the user (e.g., JWT). This token should contain information about the user’s identity and any relevant data.

B. User Sign-In

• Your server should receive sign-in requests with the user’s credentials.
• Validate the credentials against your user database.
• If the sign-in is successful, generate a custom token for the user.

3. Integrate with Firebase

• **Client-Side (Web/Mobile)**:
  • Use Firebase Authentication SDK to sign in using your custom auth provider.
  • In the client application, handle user interactions to gather sign-up or sign-in credentials (e.g., using forms or UI elements).
  • Once the credentials are gathered, make an API call to your server’s authentication endpoint.
  • On successful authentication, your server will return the custom token.
  • Use Firebase Authentication SDK to sign in with the custom token using the following code snippet (JavaScript Example):

firebase.auth().signInWithCustomToken(customToken)
.then((userCredential) => {
// User signed in successfully
const user = userCredential.user;
console.log('User signed in successfully:', user);
})
.catch((error) => {
// Handle Errors
console.error('Error signing in with custom token:', error);
});

4. Secure Your API

To protect your server and user data, use Firebase Admin SDK to verify the custom token and ensure only authorized users access your API.

const admin = require('firebase-admin');

// Initialize the Firebase Admin SDK
admin.initializeApp({
// Your Firebase project configuration
});

// Verify the custom token
admin.auth().verifyIdToken(idToken)
.then((decodedToken) => {
const uid = decodedToken.uid;
console.log('UID:', uid);
// Access the user's info
// Perform actions based on the user's role
})
.catch((error) => {
// Handle error
});

Example: Implementing Custom Phone Authentication

Here’s a simple example using Node.js and Express for custom phone authentication using Firebase:

Server (Node.js with Express)

const express = require('express');
const admin = require('firebase-admin');
const bodyParser = require('body-parser');
const twilio = require('twilio'); // Assuming you use Twilio for SMS

// Replace with your Firebase project credentials
const serviceAccount = require('./path/to/serviceAccountKey.json');

admin.initializeApp({
credential: admin.credential.cert(serviceAccount),
databaseURL: 'your-firebase-project-url.firebaseio.com' // Replace with your project URL
});

// Create an Express app
const app = express();

// Use body-parser to parse request bodies
app.use(bodyParser.json());

// Replace with your Twilio account SID and auth token
const twilioClient = new twilio(
'ACxxxxxxxxxxxxxxxxxxxxx', // Account SID
'your_auth_token' // Auth Token
);

// Send SMS Verification Code
app.post('/send-verification-code', async (req, res) => {
const phoneNumber = req.body.phoneNumber;
try {
// Generate a random 6-digit verification code
const code = Math.floor(100000 + Math.random() * 900000);

// Send SMS via Twilio
await twilioClient.messages.create({
body: `Your verification code is ${code}`,
from: '+11234567890', // Replace with your Twilio phone number
to: phoneNumber,
});

// Store the code in your database or session for verification
// (replace with your actual database logic)
await db.collection('users').doc(phoneNumber).set({
verificationCode: code
});

res.status(200).send({ message: 'Verification code sent successfully' });
} catch (error) {
console.error(error);
res.status(500).send({ message: 'Error sending verification code' });
}
});

// Verify Phone Number
app.post('/verify-phone', async (req, res) => {
const phoneNumber = req.body.phoneNumber;
const enteredCode = req.body.code;

try {
// Retrieve stored verification code from database
const userDoc = await db.collection('users').doc(phoneNumber).get();
const storedCode = userDoc.data().verificationCode;

if (enteredCode === storedCode) {
// Phone number is verified
// Generate a custom token (JWT)
const customToken = await admin.auth().createCustomToken(phoneNumber);

// Send the custom token to the client
res.status(200).send({ token: customToken });
} else {
res.status(401).send({ message: 'Invalid verification code' });
}
} catch (error) {
console.error(error);
res.status(500).send({ message: 'Error verifying phone number' });
}
});

// Start the server
app.listen(3000, () => {
console.log('Server listening on port 3000');
});

Client (JavaScript)

// Initialize Firebase
firebase.initializeApp(firebaseConfig);

// Function to sign in with custom token
async function signInWithCustomToken() {
const phoneNumber = document.getElementById('phoneNumber').value;
const code = document.getElementById('verificationCode').value;

try {
// Send verification code
const response = await fetch('/send-verification-code', {
method: 'POST',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify({ phoneNumber: phoneNumber })
});

// Handle sending verification code response
if (response.ok) {
// ...
} else {
// Handle error
}

// Verify phone number
const verificationResponse = await fetch('/verify-phone', {
method: 'POST',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify({ phoneNumber: phoneNumber, code: code })
});

// Handle verification response
if (verificationResponse.ok) {
const data = await verificationResponse.json();
const customToken = data.token;

// Sign in with the custom token
firebase.auth().signInWithCustomToken(customToken)
.then((userCredential) => {
// User signed in successfully
const user = userCredential.user;
console.log('User signed in successfully:', user);
})
.catch((error) => {
// Handle Errors
console.error('Error signing in with custom token:', error);
});
} else {
// Handle error
}
} catch (error) {
// Handle Errors
console.error('Error signing in:', error);
}
}

User Interface

You would need to create an HTML form to gather phone number and verification code inputs, and a button to trigger the authentication process.

Key Considerations

• Token Security: Always protect your custom tokens and ensure they are not easily intercepted or compromised.
• Authentication Flow: Implement a clear authentication flow, including error handling, user feedback, and security measures.
• Scalability: Design your custom authentication system to be scalable and able to handle a large number of users.

Comparison of Built-in Providers and Custom Auth

Conclusion

Integrating a custom auth provider with Firebase provides flexibility and control over your user authentication system. By implementing your authentication logic, generating custom tokens, and integrating with Firebase Authentication, you can leverage the benefits of Firebase while tailoring your authentication experience to your specific needs.