As a workaround -- If you manually define a VERCEL environment variable for development in your Vercel project with an empty value, the warning does not appear

Pretty sure this is the offending line of code:

@markflorkowski - Removing Vercel="1" is a nice way to get rid of the warning.

It looks like the detect-host function is ultimately responsible for this issue.

Detect host function checks for that env variable, assumes the code is running on Vercel and returns the forwarded host. When running locally, this is empty. @momotofu, thanks for showing where the assertion happens.

I wonder if that function should check for NEXTAUTH_URL and fallback to the Vercel forwarded host. This would allow next-auth specific configuration to take precedence over platform specific hooks instead of the other way around. Just an idea.

I've noticed that behavior as well. The use-case I have is that disabled the Git integration of Vercel with GitHub in favor of the Vercel CLI in the GitHub workflows. Within the script I do a vercel pull --environment=production prior to building. Since the respective env file contains a bunch of VERCEL_ in addition to a VERCEL variable the NextAuth package is really having a hard time.

Usually NEXTAUTH_URL is set to VERCEL_URL should that be defined. However if NEXTAUTH_URL isn't explicitly set and VERCEL_URL is set to the empty string (after pulling the variables) Next.js itself fails the build process with an Invalid URL error during the final step where the built output is checked.

My current workaround is to pull the variables and apply the following script in the pipeline to remove all Vercel variables:

const envfile = require('envfile');
const fs = require('fs');
const path = require('path');

(() => {
  const envPaths = [
    path.join(__dirname, '..', '.vercel', '.env.production.local'),
    path.join(__dirname, '..', '.vercel', '.env.preview.local'),
    path.join(__dirname, '..', '.vercel', '.env.development.local'),
    path.join(__dirname, '..', '.env'),
  ];
  envPaths
    .filter((filePath) => fs.existsSync(filePath))
    .forEach((filePath) => {
      const file = fs.readFileSync(filePath);
      const config = envfile.parse(file.toString());
      const fixedConfig = Object.entries(config)
        .filter(([key]) => !key.startsWith('VERCEL'))
        .reduce((obj, [key, value]) => ({ ...obj, [key]: value }), {});
      fs.writeFileSync(filePath, envfile.stringify(fixedConfig));
    });
})();

Basically the URL handling within the library is really difficult to understand as it's not easy in the first place to handle all environments correctly.

Worked for me.

NOT SOLVED

how can you change that in production?

dude i fixed my code by shift the .env from apps to root folder of nextjs

how i m using docker deplyment option