Vercel

If acme.com is a Next.js app on Vercel, a middleware.ts rewrite forwards /docs/* to your NookDocs origin. See Host at a subpath for the overall model.

middleware.ts

Add this to your Next.js app (replace origin/domain/path):

// middleware.ts
import { NextResponse } from "next/server";

export const config = { matcher: "/docs/:path*" };

export function middleware(request: Request) {
  const url = new URL(request.url);
  url.hostname = "acme.nookdocs.site";
  url.protocol = "https:";
  url.port = "";
  const headers = new Headers(request.headers);
  headers.set("X-Nookdocs-Host", "acme.com");
  headers.set("X-Nookdocs-Base-Path", "/docs");
  return NextResponse.rewrite(url, { request: { headers } });
}

Why middleware, not rewrites

vercel.json / next.config.js rewrites can forward the path but can't set request headers, and we need X-Nookdocs-Host + X-Nookdocs-Base-Path. Middleware's NextResponse.rewrite(url, { request: { headers } }) does both — it proxies to the external origin and attaches the headers.

Verify

curl -sI https://acme.com/docs | grep -i content-type
curl -s  https://acme.com/docs/llms.txt | head -1

Notes

• The matcher scopes the middleware to /docs/* only — the rest of your app is untouched.

• Not a Next.js app? Use Cloudflare Workers or AWS CloudFront in front of any stack.

• Sending a CSP? See CSP configuration.