Protected routes with middleware in NextJS - Step-by-Step Execution

Concept Flow - Protected routes with middleware

User Request URL

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Middleware Intercepts Request

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Check Authentication Token

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Allow Access

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Render Page

The middleware checks if the user is authenticated before allowing access to protected pages. If not authenticated, it redirects to login.

Execution Sample

NextJS

import { NextResponse } from 'next/server';

export function middleware(request) {
  const pathname = request.nextUrl.pathname;
  if (pathname.startsWith('/dashboard') || pathname.startsWith('/profile')) {
    const token = request.cookies.get('token');
    if (!token) return NextResponse.redirect(new URL('/login', request.url));
  }
  return NextResponse.next();
}

Middleware checks for a token cookie; if missing, redirects to login; otherwise, allows the request.

Execution Table

Step	Request URL	Token Present?	Action Taken	Result
1	/dashboard	No	Redirect to /login	User sent to login page
2	/dashboard	Yes	Allow access	Dashboard page rendered
3	/profile	No	Redirect to /login	User sent to login page
4	/profile	Yes	Allow access	Profile page rendered
5	/login	No	Allow access	Login page rendered
6	/login	Yes	Allow access	Login page rendered

💡 Middleware stops by either redirecting unauthenticated users or allowing authenticated users to proceed.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6
token	undefined	undefined	string_token	undefined	string_token	undefined	string_token
request.url	/dashboard	/dashboard	/dashboard	/profile	/profile	/login	/login
action	none	redirect	allow	redirect	allow	allow	allow

Key Moments - 2 Insights

Why does the middleware redirect some requests but not others?

Because the middleware checks if the token cookie exists (see execution_table rows 1 and 2). If no token, it redirects to login; if token exists, it allows access.

What happens if a user tries to access the login page while authenticated?

The middleware allows access (see execution_table rows 5 and 6). Middleware does not block login page regardless of token presence.

Visual Quiz - 3 Questions

Look at the execution table, what action is taken at step 3 when token is missing?

A Render dashboard

B Redirect to /login

C Allow access

D Throw error

💡 Hint

Check the 'Action Taken' column at step 3 in the execution_table.

At which step does the middleware allow access to the profile page with a token?

A Step 4

B Step 3

C Step 5

D Step 6

💡 Hint

Look for the row with Request URL '/profile' and Token Present? 'Yes' in the execution_table.

If the token cookie is always missing, what will happen to requests for protected pages?

A They will cause an error

B They will be allowed

C They will be redirected to /login

D They will load normally

💡 Hint

Refer to the 'Token Present?' and 'Action Taken' columns in the execution_table for missing tokens.

Concept Snapshot

Protected routes use middleware to check authentication.
Middleware runs before page loads.
If token cookie missing, redirect to login.
If token present, allow page access.
This protects pages from unauthenticated users.

Full Transcript

This visual execution shows how Next.js middleware protects routes by checking for an authentication token cookie. When a user requests a page, the middleware intercepts the request and looks for the token. If the token is missing, the middleware redirects the user to the login page. If the token exists, the middleware allows the request to continue and the page renders normally. The execution table traces requests to different URLs with and without tokens, showing when redirects happen and when access is allowed. The variable tracker shows how the token and action variables change at each step. Key moments clarify why redirects happen and how login page access is handled. The quiz tests understanding of middleware decisions based on token presence. This helps beginners see step-by-step how protected routes work in Next.js middleware.