How to implement serverless authentication with Firebase Authentication in a Nest.js application

Implementing serverless authentication with Firebase Authentication in a Nest.js application involves using Firebase Authentication to handle user authentication and integrating it into your Nest.js application. Here's a step-by-step guide to achieve this:

1. Set up Firebase Project:

   If you haven't already, set up a Firebase project in the Firebase Console. Enable Firebase Authentication in your project and configure authentication methods (e.g., email/password, Google sign-in, etc.) as per your requirements.

2. Install Firebase SDK:

   Install the Firebase Admin SDK in your Nest.js project to interact with Firebase services programmatically.

   bashCopy code
   npm install firebase-admin
   

3. Initialize Firebase Admin SDK:

   Initialize Firebase Admin SDK in your Nest.js application. You'll need to download the service account key JSON file from the Firebase Console and store it securely in your project directory.

   typescriptCopy code
   // firebase.service.ts
   
   import * as admin from 'firebase-admin';
   
   const serviceAccount = require('./path/to/serviceAccountKey.json');
   
   admin.initializeApp({
       credential: admin.credential.cert(serviceAccount),
       // Add any other configuration options here
   });
   
   export const firebaseAdmin = admin;
   

4. Implement Authentication Logic:

   Create services or controllers in your Nest.js application to handle user authentication using Firebase Authentication. You can use the Firebase Admin SDK to interact with Firebase Authentication APIs.

   typescriptCopy code
   // auth.service.ts
   
   import { Injectable } from '@nestjs/common';
   import { firebaseAdmin } from './firebase.service';
   
   @Injectable()
   export class AuthService {
       async verifyToken(idToken: string): Promise<string | null> {
           try {
               const decodedToken = await firebaseAdmin.auth().verifyIdToken(idToken);
               return decodedToken.uid;
           } catch (error) {
               console.error('Error verifying token:', error);
               return null;
           }
       }
   }
   

5. Use Authentication Service:

   Use the authentication service you've created in your controllers to handle authentication for incoming requests.

   typescriptCopy code
   // auth.controller.ts
   
   import { Controller, Get, Headers } from '@nestjs/common';
   import { AuthService } from './auth.service';
   
   @Controller('auth')
   export class AuthController {
       constructor(private readonly authService: AuthService) {}
   
       @Get('verify')
       async verifyToken(@Headers('Authorization') idToken: string) {
           if (!idToken) {
               return { message: 'Authorization header is missing' };
           }
   
           // Extract the token from the Authorization header (e.g., 'Bearer <token>')
           const token = idToken.split(' ')[1];
           const userId = await this.authService.verifyToken(token);
           if (userId) {
               return { userId };
           } else {
               return { message: 'Invalid token' };
           }
       }
   }
   

6. Protect Routes:

   You can protect routes by adding guards or middleware to verify user authentication before allowing access.

7. Deploy Your Nest.js Application:

   Deploy your Nest.js application to a serverless platform like AWS Lambda, Azure Functions, or Google Cloud Functions.

8. Configure CORS (Optional):

   If your Nest.js application and Firebase Authentication are hosted on different domains, configure CORS to allow cross-origin requests.

That's it! You've now implemented serverless authentication with Firebase Authentication in your Nest.js application. Adjust the implementation according to your specific requirements and security considerations.