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Securing Next.js APIs with Firebase Authentication

At, we've gleaned substantial expertise from developing over 30 projects utilizing technologies like Next.js and Firebase. In this tutorial, we'll discuss how to leverage Firebase Authentication to secure your Next.js API endpoints. This setup is pivotal for any web application that requires user authentication before accessing certain resources.

Understanding the Code Snippet

Here is a breakdown of what each part of the code provided does:

import { NextApiRequest, NextApiResponse } from 'next';
import { getApp, initializeApp, getApps, cert } from 'firebase-admin/app';
import { getAuth } from 'firebase-admin/auth';
import serviceAccount from '../../serviceAccountKey.json';

if (getApps().length === 0) {
  initializeApp({ credential: cert(serviceAccount) });

export default async function verifyToken(req: NextApiRequest, res: NextApiResponse) {
  const { authorization } = req.headers;
  if (!authorization) {
    return res.status(400).json({ error: 'No authorization headers provided' });

  const token = authorization.split(' ')[1];
  if (!token) {
    return res.status(401).json({ message: 'No token provided' });

  try {
    const decodedToken = await getAuth().verifyIdToken(token);
    req.user = decodedToken;
  } catch (error) {
    res.status(403).json({ error: 'Invalid or expired token' });
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  1. Firebase Setup: Initializes Firebase Admin SDK if it's not already initialized. This is crucial for server-side operations.
  2. API Endpoint: The verifyToken function serves as an API endpoint within a Next.js application. It checks for the presence of an authorization header.
  3. Token Verification: Extracts the token from the header, and uses Firebase to verify it. If the token is valid, it attaches the decoded information to the request, otherwise, it sends an error response.

Use Cases

Such an API endpoint can be used in various scenarios, including but not limited to:

  • Protecting sensitive endpoints that should only be accessible to authenticated users.
  • Serving as a middleware for other APIs within your application, ensuring they are secure.

Deployment Considerations

When deploying your application, ensure that serviceAccountKey.json is securely managed and not exposed publicly. Additionally, regularly update your Firebase Admin SDK and monitor for any authentication anomalies.


Implementing Firebase Authentication within your Next.js applications is an effective strategy to enhance security. For a hands-on demonstration of this code in action, consider visiting some of our innovative solutions such as free online video compression, temporary email services, and a tool for finding adjectives. These platforms utilize various forms of authentication and security measures to safeguard user interactions.

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