How to implement authentication in Next.js



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Next.js, being a React framework, doesn't have built-in authentication, but you can implement it using various authentication providers or custom solutions. Here, I'll outline a general approach using a popular authentication library called NextAuth.js along with a custom server.

Steps to Implement Authentication in Next.js using NextAuth.js:

Step 1: Install Dependencies

Install the necessary packages:

bash
npm install next-auth

Step 2: Create a Custom Server

Next.js requires a custom server for certain advanced features like authentication. Create a file named server.js in your project root:

javascript
// server.js
const express = require('express');
const { createServer } = require('http');
const { parse } = require('url');
const next = require('next');
const nextAuth = require('next-auth');
const nextAuthConfig = require('./next-auth-config');

const dev = process.env.NODE_ENV !== 'production';
const app = next({ dev });
const handle = app.getRequestHandler();

app.prepare().then(() => {
  const server = express();

  server.use(
    nextAuth({
      ...nextAuthConfig,
      pages: {
        signIn: '/auth/signin',
        signOut: '/auth/signout',
        error: '/auth/error',
        verifyRequest: '/auth/verify-request',
        newUser: null, // Will disable the default new account creation screen
      },
    })
  );

  server.all('*', (req, res) => {
    const parsedUrl = parse(req.url, true);
    handle(req, res, parsedUrl);
  });

  createServer(server).listen(3000, (err) => {
    if (err) throw err;
    console.log('> Ready on http://localhost:3000');
  });
});

Step 3: Create a NextAuth Config File

Create a file named next-auth-config.js in your project root:

javascript
// next-auth-config.js
export default {
  providers: [
    // Add your authentication providers here (e.g., Google, GitHub, etc.)
    // Example with Google provider:
    // {
    //   id: 'google',
    //   name: 'Google',
    //   type: 'oauth',
    //   version: '2.0',
    //   scope: 'openid profile email',
    //   clientId: 'YOUR_GOOGLE_CLIENT_ID',
    //   clientSecret: 'YOUR_GOOGLE_CLIENT_SECRET',
    // },
  ],
  callbacks: {
    async session(session, user) {
      return Promise.resolve({
        ...session,
        user: {
          ...session.user,
          id: user.id,
        },
      });
    },
  },
};

Add the necessary provider configurations for the authentication providers you want to use.

Step 4: Add Authentication to Pages

You can protect your pages by adding authentication checks. For example:

jsx
// pages/dashboard.js
import { useSession } from 'next-auth/react';

function Dashboard() {
  const { data: session } = useSession();

  if (!session) {
    return <p>You need to be authenticated to access this page.</p>;
  }

  return (
    <div>
      <h1>Dashboard</h1>
      <p>Welcome, {session.user.name}!</p>
    </div>
  );
}

export default Dashboard;

Step 5: Update package.json

Update your package.json to use the custom server:

json
"scripts": {
  "dev": "node server.js",
  "build": "next build",
  "start": "NODE_ENV=production node server.js"
}

Step 6: Start the Application

Run your application:

bash
npm run dev

This setup allows you to add authentication to your Next.js application using NextAuth.js and custom server configuration. Adjust the configuration and providers according to your needs.

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