Authentication in Next Js

Authentication is a crucial aspect of any web application that involves user accounts and personal data. It ensures that only authorized users have access to the protected resources and prevents unauthorized access and misuse of sensitive information. In this blog, we will discuss how to implement authentication using Next.js, a popular framework for building server-side rendered React applications.

Before we dive into the details of implementing authentication, let’s first understand the basic concepts of authentication. Authentication is the process of verifying the identity of a user or system. It involves two parties – the user and the system. The user provides their credentials, such as a username and password, and the system verifies them to grant access.

There are various types of authentication mechanisms, including:

  • Password-based authentication: The user provides a password that is verified against a stored hash of the password.
  • Token-based authentication: The user provides a token that is verified against a stored token on the server.
  • Multi-factor authentication: The user provides multiple forms of identification, such as a password and a code sent to their phone.

Next.js provides built-in support for server-side rendering and client-side rendering, making it an ideal choice for implementing authentication in a web application. Let’s see how we can implement authentication in Next.js using some popular libraries and techniques.

  1. Using NextAuth.js NextAuth.js is a popular library for implementing authentication in Next.js applications. It provides a simple and easy-to-use interface for implementing authentication using various providers such as Google, Facebook, Twitter, etc. The library supports multiple authentication mechanisms such as email and password-based authentication, token-based authentication, and social login.

To use NextAuth.js, we first need to install it using npm:

npm install next-auth

Once installed, we can configure NextAuth.js by creating a file called [...nextauth].js in the pages/api/auth directory. This file contains the configuration for NextAuth.js and is used to define the authentication providers and the callback functions.

Here’s an example of how we can configure NextAuth.js for email and password-based authentication:

import NextAuth from 'next-auth';
import Providers from 'next-auth/providers';

export default NextAuth({
  providers: [
      server: {
        host: process.env.EMAIL_SERVER_HOST,
        port: process.env.EMAIL_SERVER_PORT,
        auth: {
          user: process.env.EMAIL_SERVER_USER,
          pass: process.env.EMAIL_SERVER_PASSWORD,
      from: process.env.EMAIL_FROM,

  callbacks: {
    signIn: async (user, account, profile) => {
      // validate the user
      return Promise.resolve(true);

    redirect: async (url, baseUrl) => {
      return Promise.resolve(baseUrl);

    session: async (session, user) => {
      return Promise.resolve(session);

    jwt: async (token, user, account, profile, isNewUser) => {
      return Promise.resolve(token);

  database: process.env.DATABASE_URL,

In the above code, we have defined the email provider using Providers.Email. We have also defined the callback functions for signIn, redirect, session, and jwt. These functions are used to customize the authentication flow and perform additional checks on the user.

  1. Using JWT Tokens JWT (JSON Web Tokens) is a popular mechanism for implementing token-based authentication in web applications. It involves generating a token on the server and sending it to the client. The client then sends the token with every request to the server, and the server verifies the token to grant access.

To implement JWT authentication in Next.js, we can use the jsonwebtoken library to generate and verify tokens. Here’s an example of how

JSON Web Tokens (JWT) are a compact and self-contained mechanism for securely transmitting information between parties as a JSON object. They are commonly used for authentication and authorization purposes in web applications.

To implement authentication using JWT tokens in Next.js, we can use the jsonwebtoken library to generate and verify tokens. Here’s an example of how we can implement JWT authentication in Next.js:

  1. Install the jsonwebtoken library using npm:
    npm install jsonwebtoken
  2. Create a file called auth.js in the pages/api directory:
    import jwt from 'jsonwebtoken';
    const secret = 'mysecretkey'; // replace with your own secret key
    export default (req, res) => {
      if (req.method === 'POST') {
        // validate the user's credentials
        const { email, password } = req.body;
        if (email === '' && password === 'password') {
          // generate a JWT token and send it to the client
          const token = jwt.sign({ email }, secret, { expiresIn: '1h' });
          res.status(200).json({ token });
        } else {
          res.status(401).json({ message: 'Invalid credentials' });
      } else {
        res.status(405).json({ message: 'Method not allowed' });

    In the above code, we have defined an API route that handles authentication. When the user submits their credentials via a POST request, we validate their credentials and generate a JWT token using the jsonwebtoken library. We then send the token back to the client as a JSON response.

  3. Protect your API routes using JWT authentication:Once the client has obtained a JWT token, they can use it to access protected API routes. To protect your API routes using JWT authentication, you can create a higher-order function that checks the validity of the JWT token.
    import jwt from 'jsonwebtoken';
    const secret = 'mysecretkey'; // replace with your own secret key
    export const withAuth = (handler) => async (req, res) => {
      const token = req.headers.authorization?.split(' ')[1];
      if (!token) {
        res.status(401).json({ message: 'Authorization header not found' });
      try {
        const decoded = jwt.verify(token, secret);
        req.user = decoded;
        return handler(req, res);
      } catch (error) {
        res.status(401).json({ message: 'Invalid token' });

    In the above code, we have defined a higher-order function called withAuth that takes an API route handler as input. The withAuth function checks the validity of the JWT token in the Authorization header of the request. If the token is valid, it adds the decoded user information to the request object and calls the API route handler. Otherwise, it returns a 401 Unauthorized response.

    To protect your API routes using JWT authentication, you can wrap your API route handlers with the withAuth function:

    import { withAuth } from './auth';
    export default withAuth((req, res) => {
      // handle protected API route

    By using JWT tokens for authentication in your Next.js application, you can provide a secure and reliable authentication mechanism for your users.

    Thanks for reading the blog please let me know doubts in comment section.

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