Why authentication matters in NextJS

Introduction

Authentication helps confirm who you are when using a website or app. It keeps your information safe and private.

When users need to log in to access their personal dashboard.

When you want to protect sensitive data like payment details.

When you want to allow users to save their progress or preferences.

When you want to restrict certain pages to only registered users.

When you want to track user activity securely.

Syntax

NextJS

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

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

  if (session) {
    return (
      <>
        <p>Welcome, {session.user.name}!</p>
        <button onClick={() => signOut()}>Sign out</button>
      </>
    );
  }
  return <button onClick={() => signIn()}>Sign in</button>;
}

This example uses next-auth, a popular authentication library for Next.js.

useSession hook checks if the user is logged in or not.

Examples

Shows a greeting if the user is signed in, otherwise asks to sign in.

NextJS

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

function Greeting() {
  const { data: session } = useSession();
  return <p>{session ? `Hello, ${session.user.email}` : 'Please sign in'}</p>;
}

Button to sign in using GitHub as the provider.

NextJS

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

export default function SignInButton() {
  return <button onClick={() => signIn('github')}>Sign in with GitHub</button>;
}

Sample Program

This component shows a welcome message and sign out button if the user is logged in. Otherwise, it shows a sign in button.

NextJS

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

export default function AuthExample() {
  const { data: session } = useSession();

  if (session) {
    return (
      <main>
        <h1>Welcome, {session.user.name}!</h1>
        <p>You are signed in.</p>
        <button onClick={() => signOut()}>Sign out</button>
      </main>
    );
  }

  return (
    <main>
      <h1>You are not signed in.</h1>
      <button onClick={() => signIn()}>Sign in</button>
    </main>
  );
}

Important Notes

Always protect sensitive pages by checking authentication on the server or client.

Use secure cookies and HTTPS to keep user data safe.

Make sure to handle loading states when checking if a user is signed in.

Summary

Authentication confirms who a user is and protects their data.

Next.js apps use libraries like next-auth to handle authentication easily.

Always check if a user is signed in before showing private content.

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