Resolving 404 Errors with Next Auth and Custom BasePath in Next.js

Learn how to fix 404 errors when using Next Auth with a custom basePath in your Next.js application. Step-by-step guide included!
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This video is based on the question https://stackoverflow.com/q/72434552/ asked by the user 'Luis Felipe R. Hübner' ( https://stackoverflow.com/u/15268447/ ) and on the answer https://stackoverflow.com/a/75149924/ provided by the user 'Luis Felipe R. Hübner' ( https://stackoverflow.com/u/15268447/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving 404 Errors with Next Auth and Custom BasePath in Next.js

When working with Next.js applications, integrating authentication can become tricky, especially when using Next Auth alongside a custom base path. A common scenario that many developers face involves encountering 404 errors for authentication endpoints. In this guide, we’ll explore this problem and provide a detailed solution to ensure your authentication setup works flawlessly.

The Problem

Imagine you’ve built a Next.js application that authenticates users through Next Auth. You have a custom base path in your configuration, but when attempting to access the session endpoint (api/auth/session), you receive a 404 error. Here’s a breakdown of what might be wrong:

You have set a basePath in your next.config.js file. In your case, it points to a subfolder: basePath: '/twenty-test'.

Your NEXTAUTH_URL is accurately set to reflect your subdomain: NEXTAUTH_URL="https://example.com/twenty-test/api/auth".

However, attempting to navigate to this URL results in a 404 error, indicating that the expected route is not found.

Example Scenario

You might have noticed this error while trying to log in through a custom credentials provider. Consider the following example configuration for your provider:

[[See Video to Reveal this Text or Code Snippet]]

Understanding the Solution

The key to resolving this issue lies in ensuring that your application is built and configured correctly for the hosting environment. Here are the steps to troubleshoot and overcome the problem:

1. Building on the Server

One primary reason behind receiving the 404 error is that the application was built locally, which could lead to hardcoded references to localhost. When deploying your application, it’s crucial to build directly on the server environment. This guarantees that your NEXTAUTH_URL is set appropriately for the live domain.

Action Step: Access your server and initiate the build process directly there. This eliminates potential mismatches in URLs that could cause 404 errors.

2. Updating Environment Variables

If you’re unable to build on the server for any reason, another workaround is to replace instances of localhost in the environment variables after building your application. Here’s how you can do this:

Manual Adjustment: After your build is complete, search for any instances of NEXTAUTH_URL that reference localhost and replace them with the correct server URL.

Automation: Consider using a post-build script to automate the URL replacement, reducing the manual workload.

3. Ensure Proper Configuration

Finally, make sure the following configurations in your next.config.js are correct:

[[See Video to Reveal this Text or Code Snippet]]

Additionally, check your environment variable setup for NEXTAUTH_URL:

[[See Video to Reveal this Text or Code Snippet]]

Ensure these settings are accurately reflecting the live environment and not pointing to development URLs.

Conclusion

Integrating Next Auth with a custom base path in Next.js might induce some challenges initially, particularly with 404 endpoint errors resulting from mismatched environment variables or URLs. By carefully managing your build process and ensuring your configurations are correctly set, you can easily navigate past these stumbling blocks.

The important takeaway is to build your application on the server where it will be deployed whenever possible. With these strategies in hand, your authentication setup should function smoothly, driving user confidence in your application’s security.

Feel free to share your experiences or additional questions in the comments below!

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