Why authentication matters in NextJS - See It in Action

Why authentication matters

📖 Scenario: You are building a simple Next.js app that shows a secret message only to logged-in users. This helps protect private information from strangers.

🎯 Goal: Create a Next.js component that checks if a user is logged in and shows a secret message only when authenticated.

📋 What You'll Learn

Create a variable to represent user login status

Add a configuration variable for the secret message

Use conditional rendering to show the secret message only if the user is logged in

Complete the component with a return statement that renders the message or a login prompt

💡 Why This Matters

🌍 Real World

Authentication is essential to protect private data in web apps, like user profiles, messages, or payment info.

💼 Career

Understanding authentication basics helps you build secure web applications and work with user sessions in real projects.

1

DATA SETUP: Create a variable for user login status

Create a constant called isLoggedIn and set it to false to represent that the user is not logged in yet.

NextJS

// Your code here

Hint

Use const to create a variable named isLoggedIn and set it to false.

2

CONFIGURATION: Add a secret message variable

Create a constant called secretMessage and set it to the string 'The sky is blue.' which will be shown only to logged-in users.

NextJS

const isLoggedIn = false;
// Your code here

Hint

Use const to create secretMessage with the exact text.

3

CORE LOGIC: Use conditional rendering to show the secret message

Write a function component called SecretInfo that returns <p>Please log in to see the secret.</p> if isLoggedIn is false, otherwise returns <p>{secretMessage}</p>.

NextJS

const isLoggedIn = false;
const secretMessage = 'The sky is blue.';

// Your code here

Hint

Use a function named SecretInfo with an if statement checking !isLoggedIn to return the login prompt, else return the secret message.

4

COMPLETION: Export the component as default

Add export default SecretInfo; at the end to make the component usable in your Next.js app.

NextJS

const isLoggedIn = false;
const secretMessage = 'The sky is blue.';

function SecretInfo() {
  if (!isLoggedIn) {
    return Please log in to see the secret.;
  } else {
    return {secretMessage};
  }
}

// Your code here

Hint

Use export default SecretInfo; to export the component.

Practice

1. Why is authentication important in a Next.js application?

easy

A. It automatically fixes bugs in the code.

B. It speeds up the loading time of pages.

C. It confirms the identity of users and protects private data.

D. It changes the app's color scheme based on user preference.

Solution

1. Step 1: Understand the purpose of authentication

   Authentication is used to confirm who a user is when they access an app.

2. Step 2: Recognize the importance of protecting data

   It helps protect private or sensitive data by allowing only authorized users to see it.

3. Final Answer:

   It confirms the identity of users and protects private data. -> Option C

4. Quick Check:

   Authentication = Confirm identity and protect data [OK]

Hint: Authentication means confirming who the user is [OK]

Common Mistakes:

• Confusing authentication with app speed
• Thinking authentication changes UI colors
• Believing authentication fixes code bugs

2. Which of the following is the correct way to import the NextAuth library in a Next.js app?

easy

A. require('next-auth');

B. include 'next-auth';

C. import nextAuth from 'next-auth';

D. import NextAuth from 'next-auth';

Solution

1. Step 1: Identify the ES module import syntax

   Next.js uses ES module syntax with import to load libraries.

2. Step 2: Match the correct import statement

   The correct import is import NextAuth from 'next-auth'; with exact casing and syntax.

3. Final Answer:

   import NextAuth from 'next-auth'; -> Option D

4. Quick Check:

   Use ES module import syntax for NextAuth [OK]

Hint: Use ES module import, not require or include [OK]

Common Mistakes:

• Using CommonJS require instead of import
• Wrong casing in import statement
• Using include which is not valid in JS

3. Given this Next.js code snippet using next-auth, what will be rendered if the user is not signed in?

import { useSession } from 'next-auth/react';

export default function Profile() {
  const { data: session } = useSession();
  if (!session) {
    return <p>Please sign in to view your profile.</p>;
  }
  return <p>Welcome, {session.user.name}!</p>;
}

medium

A. Please sign in to view your profile.

B. Loading user data...

C. Welcome, [user's name]!

D. Error: session not found

Solution

1. Step 1: Check the session state when user is not signed in

   If the user is not signed in, session will be null or undefined.

2. Step 2: Follow the conditional rendering logic

   The code returns the message <p>Please sign in to view your profile.</p> when !session is true.

3. Final Answer:

   Please sign in to view your profile. -> Option A

4. Quick Check:

   Not signed in = show sign-in prompt [OK]

Hint: If no session, show sign-in message [OK]

Common Mistakes:

• Assuming user name shows without sign-in
• Expecting loading text instead of sign-in prompt
• Thinking an error will be thrown

4. What is wrong with this Next.js authentication check?

import { useSession } from 'next-auth/react';

export default function Dashboard() {
  const session = useSession();
  if (!session) {
    return <p>Access denied.</p>;
  }
  return <p>Dashboard content</p>;
}

medium

A. The session variable should be declared with var.

B. useSession must be destructured to get data property.

C. The component should be a class component.

D. The return statements should be inside useEffect.

Solution

1. Step 1: Check how useSession is used

   useSession returns an object with a data property containing the session info.

2. Step 2: Identify the correct destructuring

   The code should use const { data: session } = useSession(); to get the session data.

3. Final Answer:

   useSession must be destructured to get data property. -> Option B

4. Quick Check:

   Destructure useSession to access session data [OK]

Hint: Destructure useSession to get session data [OK]

Common Mistakes:

• Using useSession without destructuring
• Trying to put return inside useEffect
• Thinking class components are required
• Using var instead of const or let

5. You want to protect a Next.js page so only signed-in users can access it. Which approach correctly enforces this using next-auth?

hard

A. Use getServerSideProps to check session and redirect if not signed in.

B. Render the page normally and hide content with CSS if user is not signed in.

C. Use a client-side setTimeout to check session after page loads.

D. Allow all users to access and show an alert if not signed in.

Solution

1. Step 1: Understand server-side protection

   Using getServerSideProps allows checking the session before rendering the page.

2. Step 2: Redirect unauthorized users

   If no session is found, redirecting to sign-in page prevents unauthorized access securely.

3. Final Answer:

   Use getServerSideProps to check session and redirect if not signed in. -> Option A

4. Quick Check:

   Server-side session check = secure page protection [OK]

Hint: Check session server-side to protect pages [OK]

Common Mistakes:

• Hiding content with CSS does not secure data
• Using client-side delay risks exposing content
• Allowing access and just showing alerts is insecure