When using Next.js with NextAuth.js, you can customize the user object that is returned by NextAuth.js by adding additional properties to it when the account is created. The user object represents the authenticated user and contains various user information.

To achieve this, you can use the callbacks option provided by NextAuth.js. Specifically, you can use the session callback to modify the user object after authentication and before it is stored in the session.

Here's an example of how you can add properties to the user object when the account is created:

// pages/api/auth/[...nextauth].js import NextAuth from 'next-auth'; import Providers from 'next-auth/providers'; import { createUser } from '../../../utils/db'; // Import your function to create a user in the database export default NextAuth({ providers: [ // Configure your authentication providers here Providers.Google({ clientId: process.env.GOOGLE_CLIENT_ID, clientSecret: process.env.GOOGLE_CLIENT_SECRET, }), // Add other providers as needed ], callbacks: { async session(session, user) { // If the user object does not have the custom property "isAdmin", set it based on your logic if (!user.isAdmin) { // For example, you could check if the user email is from a certain domain to set "isAdmin" to true // In this example, we'll just set it to false user.isAdmin = false; } // Return the modified user object return Promise.resolve({ ...session, user }); }, async jwt(token, user) { // If a user object is present, add the custom property "isAdmin" to the JWT token if (user) { token.isAdmin = user.isAdmin || false; } // Return the modified token return Promise.resolve(token); }, async signIn(user, account, profile) { // Create a new user in your database with custom properties if it doesn't exist // Use your custom logic here to determine the properties of the user // This example assumes the "createUser" function creates a user in the database await createUser(user); return Promise.resolve(true); }, }, });

In the above example, we define the signIn callback to create a user in the database when they sign in. You can modify this logic to create users in your database and add any additional properties you need.

The session callback is used to add the custom properties to the user object in the session. The jwt callback is used to add the custom properties to the JSON Web Token (JWT) token, which is used to maintain the user's session state.

Remember to replace createUser with your actual function that handles user creation in your database. Additionally, customize the logic inside the session and jwt callbacks to set the custom properties based on your specific requirements.

By using these callbacks, you can easily customize the user object and add properties when the account is created in NextAuth.js.

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