Serve your site under a path with Astro

import type { APIRoute } from "astro";

const NOTRA_SITE = "https://acme.notra.site";

// Headers for this hop only, plus your visitors' sessions.
const DROPPED_REQUEST_HEADERS = [
  "host", "connection", "keep-alive", "transfer-encoding", "upgrade",
  "te", "trailer", "proxy-authorization", "content-length",
  "cookie", "authorization",
];
// fetch() decodes compressed bodies, so these no longer match.
const DROPPED_RESPONSE_HEADERS = ["content-encoding", "content-length", "transfer-encoding", "connection"];

export const proxyToNotra: APIRoute = async ({ request, clientAddress }) => {
  const url = new URL(request.url);
  const headers = new Headers(request.headers);
  for (const name of DROPPED_REQUEST_HEADERS) headers.delete(name);
  // Overwritten, so visitors can't send their own.
  headers.set("x-forwarded-for", clientAddress);

  const hasBody = request.method !== "GET" && request.method !== "HEAD";
  const upstream = await fetch(`${NOTRA_SITE}${url.pathname}${url.search}`, {
    method: request.method,
    headers,
    body: hasBody ? await request.arrayBuffer() : undefined,
    redirect: "manual",
  });

  const responseHeaders = new Headers(upstream.headers);
  for (const name of DROPPED_RESPONSE_HEADERS) responseHeaders.delete(name);
  // Keep Notra's 404 pages instead of src/pages/404.astro.
  responseHeaders.set("X-Astro-Reroute", "no");

  return new Response(upstream.body, { status: upstream.status, headers: responseHeaders });
};

import { proxyToNotra } from "../../lib/notra-proxy";

export const prerender = false;
export const ALL = proxyToNotra;