proxy.js

/**
 * An object with different URLs to fetch
 * @param {Object} ORIGINS
 */

const ORIGINS = {
  "api.tweeter.workers.dev": "api.twitter.com",
  // "root.tweeter.workers.dev": "twitter.com"
}

async function handleRequest(request) {
  const url = new URL(request.url)
  // Check if incoming hostname is a key in the ORIGINS object
  if (url.hostname in ORIGINS) {
    const target = ORIGINS[url.hostname]
    url.hostname = target
    request = new Request(url, request)
    request.headers.set("Origin", new URL(url).origin)
    // If it is, proxy request to that third party origin
    return await fetch(url.toString(), request)
  }
  else {
    url.hostname = url.searchParams.get("host")
    return await fetch(url.toString(), request)
  }
}

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