How to Link Users Across Different Authentication Providers in Next.js?

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Hi everyone,

I’m working on a Next.js app and have successfully implemented email/password authentication, which is working fine. Recently, I added Google SSO to allow users to log in with their Gmail accounts, and that’s also functioning as expected.

However, I’ve run into an issue:

When an existing user who originally registered with email/password tries to log in using Google SSO with the same email, a new user account is created instead of linking to their existing account.

I’d like to enable users to access their account through any authentication method (email/password or Google SSO) without creating duplicate accounts.

Could anyone guide me on how to link users across different authentication providers? Are there best practices, libraries, or strategies I should follow?

Thanks in advance for your help!

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To link users across different authentication providers (email/password and Google SSO) in Next.js, you can implement a strategy to associate the same user account with both login methods. Here’s a basic outline of the approach:

  1. Identify the user by email: When a user logs in via Google SSO, you can check if an account with the same email exists in your database (from email/password registration).
  2. Link the accounts: If the user is already registered via email/password, update the existing record to link the Google SSO account, typically by storing the Google ID or other unique identifier in the user record.
  3. Use a session or JWT: After successful login, use the session or JWT token to track which authentication method was used, and ensure that the user is authenticated properly across both login methods.

Strategy:

  • Database model: Ensure your user model supports multiple authentication methods (e.g., a field for googleId, email, and passwordHash).
  • Authentication flow: When a user signs in with Google, check if an account with their email exists. If it does, associate the Google login with their existing account; if not, create a new user.
  • Libraries: Use a library like NextAuth.js that supports multiple authentication providers and can help handle account linking and management.