Custom server dynamic routing

[amfeng]

Hello friends!

Following in the footsteps of Next.js' custom server example, I was hoping to implement custom domains (and dynamic subdomains) by writing a custom server and explicitly calling render on a specific path, like so:

 server.all('*', (req, res) => {
    var hostname = req.headers.host;

    // Force go to /user/customdomain if the host is the user's registered domain name or subdomain
    if (hostname == 'customdomain.com') {
      return app.render(req, res, '/user/customdomain')
    }

    // Otherwise let the Next.js server handle the request as normal
    return handle(req, res)
  })

When I try this out and go to customdomain.com in my browser, I get this error:

Unhandled Runtime Error
Error: The provided `as` value (/) is incompatible with the `href` value (/user/[username]). 
Read more: https://err.sh/vercel/next.js/incompatible-href-as

The error message makes sense, but I'm left wondering if there's a way to achieve what I want (customdomain.com OR username.mydomain.com => mydomain.com/user/username). I also need this to work with nested routes as well, which I hadn't figured out yet (customdomain.com/page1 => mydomain.com/user/username/page1).

Any thoughts or ideas? Thanks in advance! ❤️