NextAuth.js (Auth.js) setup in NextJS

Introduction

NextAuth.js helps you add user login and authentication easily to your Next.js app. It manages sign-in, sign-out, and user sessions securely.

You want users to log in with email or social accounts like Google or GitHub.

You need to protect pages so only signed-in users can see them.

You want to manage user sessions without building your own backend.

You want a quick way to add authentication without complex setup.

Syntax

NextJS

import NextAuth from "next-auth";
import GoogleProvider from "next-auth/providers/google";

export const authOptions = {
  providers: [
    GoogleProvider({
      clientId: process.env.GOOGLE_CLIENT_ID,
      clientSecret: process.env.GOOGLE_CLIENT_SECRET
    }),
    // add more providers here
  ],
  // other options like callbacks, pages, session
};

export default NextAuth(authOptions);

Put this code in pages/api/auth/[...nextauth].js to create the auth API route.

Use environment variables to keep your client IDs and secrets safe.

Examples

Basic setup with Google as the only sign-in provider.

NextJS

import NextAuth from "next-auth";
import GoogleProvider from "next-auth/providers/google";

export default NextAuth({
  providers: [
    GoogleProvider({
      clientId: process.env.GOOGLE_CLIENT_ID,
      clientSecret: process.env.GOOGLE_CLIENT_SECRET
    })
  ]
});

Setup with GitHub provider and JWT session strategy.

NextJS

import NextAuth from "next-auth";
import GitHubProvider from "next-auth/providers/github";

export default NextAuth({
  providers: [
    GitHubProvider({
      clientId: process.env.GITHUB_ID,
      clientSecret: process.env.GITHUB_SECRET
    })
  ],
  session: {
    strategy: "jwt"
  }
});

Sample Program

This is a complete NextAuth.js setup file for Next.js API route. It uses Google login and custom sign-in page.

NextJS

import NextAuth from "next-auth";
import GoogleProvider from "next-auth/providers/google";

export default NextAuth({
  providers: [
    GoogleProvider({
      clientId: process.env.GOOGLE_CLIENT_ID,
      clientSecret: process.env.GOOGLE_CLIENT_SECRET
    })
  ],
  pages: {
    signIn: "/auth/signin"
  }
});

Important Notes

Remember to add your environment variables in a .env.local file.

Use useSession() hook in your components to get user info and login status.

Protect pages by checking session on server or client side.

Summary

NextAuth.js makes adding login easy in Next.js apps.

Set up providers with client IDs and secrets.

Use the API route /api/auth/[...nextauth] to handle auth.

Practice

1. What is the main purpose of NextAuth.js in a Next.js application?

easy

A. To optimize images automatically

B. To manage database connections

C. To style components with CSS

D. To handle user authentication and login flows easily

Solution

1. Step 1: Understand NextAuth.js role

   NextAuth.js is a library designed to simplify adding authentication to Next.js apps.

2. Step 2: Identify main functionality

   It manages login flows, sessions, and providers for user authentication.

3. Final Answer:

   To handle user authentication and login flows easily -> Option D

4. Quick Check:

   NextAuth.js = Authentication helper [OK]

Hint: NextAuth.js is all about login and user sessions [OK]

Common Mistakes:

• Confusing NextAuth.js with styling or database tools
• Thinking it manages images or CSS
• Assuming it handles API routing unrelated to auth

2. Which file path is the correct place to create the NextAuth.js API route in a Next.js app?

easy

A. /pages/api/auth/[...nextauth].js

B. /pages/auth/nextauth.js

C. /api/auth.js

D. /pages/api/nextauth.js

Solution

1. Step 1: Recall NextAuth.js API route convention

   NextAuth.js requires a catch-all API route named [...nextauth].js inside /pages/api/auth/.

2. Step 2: Match the correct path

   Only /pages/api/auth/[...nextauth].js matches the required path: /pages/api/auth/[...nextauth].js.

3. Final Answer:

   /pages/api/auth/[...nextauth].js -> Option A

4. Quick Check:

   API route = /api/auth/[...nextauth] [OK]

Hint: NextAuth.js uses catch-all API route [...nextauth].js [OK]

Common Mistakes:

• Placing the file outside /api/auth/
• Using a non-catch-all filename
• Missing the brackets in filename

3. Given this NextAuth.js configuration snippet, what will be the value of session.user.name after a successful login?

import NextAuth from "next-auth";
import GithubProvider from "next-auth/providers/github";

export default NextAuth({
  providers: [
    GithubProvider({
      clientId: process.env.GITHUB_ID,
      clientSecret: process.env.GITHUB_SECRET
    })
  ],
  callbacks: {
    async session({ session, user }) {
      session.user.name = "CustomName";
      return session;
    }
  }
});

medium

A. The GitHub username

B. "CustomName"

C. Undefined

D. The user's email

Solution

1. Step 1: Understand the session callback

   The session callback modifies the session object before it is returned to the client.

2. Step 2: Check the modification

   It sets session.user.name explicitly to "CustomName" regardless of original data.

3. Final Answer:

   "CustomName" -> Option B

4. Quick Check:

   Session callback overrides user.name = "CustomName" [OK]

Hint: Session callback can override user data before sending [OK]

Common Mistakes:

• Assuming user.name stays as GitHub username
• Thinking session.user.name is undefined by default
• Confusing email with name property

4. You wrote this NextAuth.js provider config but get an error: TypeError: GithubProvider is not a function. What is the likely cause?

import { GithubProvider } from "next-auth/providers/github";

export default NextAuth({
  providers: [
    GithubProvider({
      clientId: process.env.GITHUB_ID,
      clientSecret: process.env.GITHUB_SECRET
    })
  ]
});

medium

A. Provider config must be inside callbacks

B. Missing environment variables

C. Incorrect import syntax; should use default import without braces

D. NextAuth must be imported from 'next-auth/client'

Solution

1. Step 1: Check import style for GithubProvider

   GithubProvider is the default export, so it should be imported without braces.

2. Step 2: Identify correct import syntax

   Use import GithubProvider from "next-auth/providers/github"; instead of curly braces.

3. Final Answer:

   Incorrect import syntax; should use default import without braces -> Option C

4. Quick Check:

   Default export = no braces in import [OK]

Hint: Default exports import without braces {} [OK]

Common Mistakes:

• Using named import syntax for default export
• Assuming environment variables cause this error
• Placing provider config inside callbacks

5. You want to add Google and GitHub login providers in NextAuth.js with environment variables. Which is the correct way to configure both providers in /pages/api/auth/[...nextauth].js?

hard

A. import GoogleProvider from "next-auth/providers/google";
import GithubProvider from "next-auth/providers/github";

export default NextAuth({
providers: [
GoogleProvider({ clientId: process.env.GOOGLE_ID, clientSecret: process.env.GOOGLE_SECRET }),
GithubProvider({ clientId: process.env.GITHUB_ID, clientSecret: process.env.GITHUB_SECRET })
]
});

B. import { GoogleProvider, GithubProvider } from "next-auth/providers";

export default NextAuth({
providers: [
GoogleProvider(process.env.GOOGLE_ID, process.env.GOOGLE_SECRET),
GithubProvider(process.env.GITHUB_ID, process.env.GITHUB_SECRET)
]
});

C. import GoogleProvider from "next-auth/providers/google";
import GithubProvider from "next-auth/providers/github";

export default NextAuth({
providers: {
google: GoogleProvider,
github: GithubProvider
}
});

D. import GoogleProvider from "next-auth/providers/google";
import GithubProvider from "next-auth/providers/github";

export default NextAuth({
providers: [
GoogleProvider,
GithubProvider
]
});

Solution

1. Step 1: Import providers correctly

   Each provider is a default export from its own module and must be imported separately.

2. Step 2: Configure providers as array with clientId and clientSecret

   Providers must be called as functions with an object containing clientId and clientSecret from environment variables.

3. Step 3: Validate options

   import GoogleProvider from "next-auth/providers/google"; import GithubProvider from "next-auth/providers/github"; export default NextAuth({ providers: [ GoogleProvider({ clientId: process.env.GOOGLE_ID, clientSecret: process.env.GOOGLE_SECRET }), GithubProvider({ clientId: process.env.GITHUB_ID, clientSecret: process.env.GITHUB_SECRET }) ] }); correctly imports and configures both providers in an array with proper keys.

4. Final Answer:

   Correct import and provider function calls with env variables -> Option A

5. Quick Check:

   Providers array with clientId/clientSecret = import GoogleProvider from "next-auth/providers/google"; import GithubProvider from "next-auth/providers/github"; export default NextAuth({ providers: [ GoogleProvider({ clientId: process.env.GOOGLE_ID, clientSecret: process.env.GOOGLE_SECRET }), GithubProvider({ clientId: process.env.GITHUB_ID, clientSecret: process.env.GITHUB_SECRET }) ] }); [OK]

Hint: Providers need clientId and clientSecret in array [OK]

Common Mistakes:

• Importing providers as named imports from a single module
• Passing env vars directly without object keys
• Using object instead of array for providers