NextAuth.js (Auth.js) setup in NextJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is NextAuth.js used for in a Next.js application?

NextAuth.js is a library that helps you add user authentication easily to your Next.js app. It manages sign-in, sign-out, and session handling.

beginner

Which file do you create to configure NextAuth.js in a Next.js app?

You create either /pages/api/auth/[...nextauth].js for the Pages Router or /app/api/auth/[...nextauth]/route.js for the App Router to configure NextAuth.js routes and options.

intermediate

How do you add a Google provider to NextAuth.js?

You import GoogleProvider from 'next-auth/providers/google' and add it to the providers array in the NextAuth configuration with your clientId and clientSecret.

intermediate

What is the purpose of the 'callbacks' option in NextAuth.js configuration?

Callbacks let you control what happens during sign-in, session creation, and JWT token handling. For example, you can add extra user info to the session.

beginner

How do you protect a page in Next.js to allow only signed-in users with NextAuth.js?

You use the useSession hook from 'next-auth/react' to check if a user is signed in. If not, you can redirect them or show a sign-in button.

Where should you place the NextAuth.js API route file in a Next.js app using the App Router?

A /app/api/auth/[...nextauth]/route.js

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

C /app/auth/[...nextauth]/route.js

D /api/auth/[...nextauth].js

In Next.js App Router, API routes go inside the /app/api folder with a route.js file.

Which hook do you use to get the current user session in a Next.js component with NextAuth.js?

A useUser()

B useAuth()

C useSession()

D useCurrentUser()

useSession() is the official hook from NextAuth.js to access the current user session.

What do you need to provide when adding an OAuth provider like Google to NextAuth.js?

A OAuth token only

B username and password

C API key only

D clientId and clientSecret

OAuth providers require clientId and clientSecret to authenticate your app with the provider.

Which NextAuth.js option allows you to customize the session object sent to the client?

A providers

B callbacks

C pages

D events

The callbacks option lets you modify the session object before it is returned to the client.

How do you sign out a user in a Next.js component using NextAuth.js?

A call signOut() from 'next-auth/react'

B call logout() from 'next-auth/client'

C redirect to /logout page

D clear cookies manually

NextAuth.js provides a signOut() function from 'next-auth/react' to handle user sign-out.

Explain the steps to set up NextAuth.js in a Next.js app using the App Router.

Think about where the API route goes and how to add providers.

Describe how you can protect a page so only signed-in users can access it using NextAuth.js.

Focus on checking session and conditional rendering.

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