## Description
I have deployed the same [application](https://github.com/dimkl/aws-clerk-nextjs) with production settings in 3 different platforms:
- [Railway App](https://railway.app/) [application link](https://aws-clerk-nextjs-production.up.railway.app/)
- [AWS Amplify](https://docs.amplify.aws/) [application link](https://main.d38v5rl8fqcx2i.amplifyapp.com/)
- [Vercel](https://vercel.com/) [application link](https://aws-clerk-nextjs-rf48tgtwp-dimkl.vercel.app/)

## Reproduction steps:
In platforms other than Vercel, when I click the Protected page like (at the center of page) I get redirected to {application_origin}?redirect_url=http%3A%2F%2Flocalhost%3A7260%2Fprotected.

## Middleware code snippet to redirect

const redirectToSignIn = ({ returnBackUrl }) => {
    const signInUrl = '/sign-in';
    const baseURL = new URL(returnBackUrl);

    const url = new URL(signInUrl, baseURL.origin);
    url.searchParams.set('redirect_url', returnBackUrl);

    return NextResponse.redirect(url.toString());
}

if (unauthorizedGuard) {
    const returnBackUrl = req.url; // http://localhost:3000/protected
    return redirectToSignIn({ returnBackUrl });
}

## Extra information
By navigating through the logs I found out that the req.nextUrl and the req.url use the localhost:3000 as hostname instead of the domains being used to access the apps. In the Vercel case, those URLs are populated correctly using the correct hostname.

I believe the issue occurs due to some header missing when the request is being proxied which is populated correctly in the Vercel platform.
Could you provide some insights about how I can make the NextJS application URLs use the correct hostname.

## Notes
- I also have a report from a customer that this also happens to any dockerized application using NextJS.
- I have checked the x-forwarded-host and it seems correct in all those cases but it's not being used.