Protected routes with middleware in NextJS

Introduction

Protected routes keep parts of your website safe. Middleware checks if a user can see a page before showing it.

You want only logged-in users to see their profile page.

You need to stop visitors from accessing admin pages.

You want to redirect users to login if they try to open a private page.

You want to check user permissions before loading certain pages.

Syntax

NextJS

import { NextResponse } from 'next/server';
import type { NextRequest } from 'next/server';

export function middleware(request: NextRequest) {
  const token = request.cookies.get('token')?.value;
  if (!token) {
    return NextResponse.redirect(new URL('/login', request.url));
  }
  return NextResponse.next();
}

export const config = {
  matcher: ['/protected-route', '/another-protected-route'],
};

Middleware runs before the page loads to check conditions.

The matcher tells Next.js which routes to protect.

Examples

Simple check for a cookie named 'auth'. Redirects to login if missing.

NextJS

export function middleware(request) {
  const isLoggedIn = Boolean(request.cookies.get('auth'));
  if (!isLoggedIn) {
    return NextResponse.redirect('/login');
  }
  return NextResponse.next();
}

Checks user role cookie to allow only admins to proceed.

NextJS

export function middleware(request) {
  const role = request.cookies.get('role')?.value;
  if (role !== 'admin') {
    return NextResponse.redirect('/not-authorized');
  }
  return NextResponse.next();
}

Sample Program

This middleware protects the '/dashboard' and '/settings' pages. If the user has no 'token' cookie, they get sent to '/login'. Otherwise, they can see the page.

NextJS

import { NextResponse } from 'next/server';
import type { NextRequest } from 'next/server';

export function middleware(request: NextRequest) {
  const token = request.cookies.get('token')?.value;
  if (!token) {
    return NextResponse.redirect(new URL('/login', request.url));
  }
  return NextResponse.next();
}

export const config = {
  matcher: ['/dashboard', '/settings'],
};

Important Notes

Middleware runs on the server side before the page loads.

Cookies are a common way to check if a user is logged in.

Always test your middleware to avoid blocking public pages by mistake.

Summary

Middleware helps protect routes by checking user info before loading pages.

Use cookies or tokens to decide if a user can access a page.

Configure which routes to protect using the matcher setting.

Practice

1. What is the main purpose of middleware in Next.js when protecting routes?

easy

A. To check user authentication before allowing access to certain pages

B. To style the pages dynamically based on user preferences

C. To preload images for faster page loading

D. To manage database connections automatically

Solution

1. Step 1: Understand middleware role

   Middleware runs before a page loads to control access or modify requests.

2. Step 2: Identify protection purpose

   In protected routes, middleware checks if a user is authenticated before allowing access.

3. Final Answer:

   To check user authentication before allowing access to certain pages -> Option A

4. Quick Check:

   Middleware protects routes by checking authentication [OK]

Hint: Middleware runs before page load to check user access [OK]

Common Mistakes:

• Thinking middleware styles pages
• Confusing middleware with database management
• Assuming middleware preloads images

2. Which of the following is the correct way to export middleware in Next.js to protect routes?

easy

A. export function middleware() { /* code */ }

B. function middleware() { /* code */ } export middleware

C. export middleware = () => { /* code */ }

D. export default function middleware(req) { /* code */ }

Solution

1. Step 1: Recall Next.js middleware export syntax

   Middleware must be exported as the default export function named middleware.

2. Step 2: Check options for correct syntax

   Only export default function middleware(req) { /* code */ } uses "export default function middleware(req)" which is valid syntax.

3. Final Answer:

   export default function middleware(req) { /* code */ } -> Option D

4. Quick Check:

   Middleware uses default export function [OK]

Hint: Middleware must be default exported as a function named middleware [OK]

Common Mistakes:

• Using named export instead of default
• Assigning middleware to a variable without export default
• Incorrect export statement syntax

3. Given this middleware code snippet, what happens when a user is not authenticated?

import { NextResponse } from 'next/server';

export default function middleware(req) {
  const token = req.cookies.get('token');
  if (!token) {
    return NextResponse.redirect(new URL('/login', req.url));
  }
  return NextResponse.next();
}

medium

A. The user stays on the current page without any change

B. The user is redirected to the /login page

C. The middleware throws an error and stops loading

D. The user is redirected to the homepage

Solution

1. Step 1: Analyze token check in middleware

   The middleware checks if the 'token' cookie exists; if not, it triggers a redirect.

2. Step 2: Understand redirect behavior

   If no token, middleware returns a redirect response to '/login' page.

3. Final Answer:

   The user is redirected to the /login page -> Option B

4. Quick Check:

   No token causes redirect to login [OK]

Hint: No token cookie means redirect to login page [OK]

Common Mistakes:

• Assuming user stays on page without token
• Thinking middleware throws error on missing token
• Confusing redirect target URL

4. Identify the error in this middleware code that aims to protect routes:

import { NextResponse } from 'next/server';

export default function middleware(req) {
  const token = req.cookies.token;
  if (!token) {
    return NextResponse.redirect('/login');
  }
  return NextResponse.next();
}

medium

A. Missing async keyword in middleware function

B. Redirect URL should be absolute, not relative

C. Accessing cookies incorrectly; should use req.cookies.get('token')

D. NextResponse.next() should be replaced with NextResponse.continue()

Solution

1. Step 1: Check cookie access method

   In Next.js middleware, cookies are accessed with req.cookies.get('token'), not req.cookies.token.

2. Step 2: Verify redirect usage

   Redirect can accept a relative path, so that is valid here.

3. Final Answer:

   Accessing cookies incorrectly; should use req.cookies.get('token') -> Option C

4. Quick Check:

   Use req.cookies.get('token') to read cookies [OK]

Hint: Use req.cookies.get('token') to read cookies in middleware [OK]

Common Mistakes:

• Using dot notation for cookies object
• Thinking redirect URL must be absolute
• Confusing NextResponse.next() with continue()

5. You want to protect only the routes starting with /dashboard using middleware. Which is the correct way to apply middleware only to these routes?

hard

A. export const config = { matcher: ['/dashboard/:path*'] };

B. export const config = { matcher: ['/dashboard*'] };

C. export const config = { matcher: ['/dashboard'] };

D. export const config = { matcher: ['/dashboard/**'] };

Solution

1. Step 1: Understand matcher pattern syntax

   The matcher uses path patterns where ':path*' matches all subpaths under /dashboard.

2. Step 2: Compare options for correct pattern

   export const config = { matcher: ['/dashboard/:path*'] }; uses '/dashboard/:path*' which correctly matches /dashboard and all nested routes.

3. Final Answer:

   export const config = { matcher: ['/dashboard/:path*'] }; -> Option A

4. Quick Check:

   Use '/dashboard/:path*' to match dashboard and subpaths [OK]

Hint: Use ':path*' to match all subpaths under a route [OK]

Common Mistakes:

• Using wildcard * without colon for subpaths
• Matching only exact /dashboard without subpaths
• Using invalid glob pattern like /**