Cloudflare Worker for SaaS provider routing without custom origin server

worker.js

// SaaS provider creates different subdomains to handle traffic of different eyeball domains
// Get rid of https://developers.cloudflare.com/cloudflare-for-platforms/cloudflare-for-saas/start/advanced-settings/custom-origin/

const ORIGINS = {
  'a.com': 'a.cicku.me',
  'b.com': 'b.cicku.me',
  'c.com': 'c.cicku.me',
  'd.com': 'd.cicku.me',
  'e.com': 'e.cicku.me',
  'f.com': 'f.cicku.me'
};
let target = ""
let response = ""

async function handleRequest(request) {
  const url = new URL(request.url);

  if (url.hostname in ORIGINS) {
    target = ORIGINS[url.hostname];
    url.hostname = target;
    response = await fetch(url.toString(), request);
  }
  else {
    response = await fetch(request);
  }
  
  const newResponse = new Response(response.body, response);
  // add a header for debugging
  newResponse.headers.append('x-origin-server', '1');
  return newResponse;
}

addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request));
});