This is a Next.js project bootstrapped with create-next-app.

First, run the development server:

npm run dev
# or
yarn dev
# or
pnpm dev

Open http:https://localhost:3000 with your browser to see the result.

The routing is set up the following way:
hostname.com/projects/{project-slug}/*.

The job of the middleware is to convert a different shape to the above shape internally. The routing that the middleware is expecting is the following:
{project-slug}.hostname.com/*

This means when you access the shape of the middleware, the server will internally rewrite the URL to the shape that Next.js is expecting (no redirect).

Custom domains from subdomains should not be an issue, as a CNAME can simply be used to point to the subdomain. Because a CNAME will still work with the original domain for the host header, this should just work.

So a CNAME for the-pigeons.ch pointing to the-pigeons.hostname.com should work.

On vercel, this setup probably won't work (due to their CNAME setup or something, did not figure it out yet). You should use A records if you want to work with custom sub.domains (just like root domains). And then add it to domains.json.

If you want to add a root domain (or you don't want to work with CNAME in general), it is a bit more complicated, since a CNAME cannot be used for root domains. The apex domain needs to be configured using an A record to point directly to the host server.

The middleware then needs to be informed about which root domains belong to which project. This is why the domains.json file exists. It is a simple JSON file that maps project slugs to root domains. It has the following shape:

{
  "project-slug": ["domain1.com", "domain2.com"]
}