Deploy a Reverse Proxy With Cloudflare Workers

This is a script running on Cloudflare Workers to make a reverse proxy.

const upstream = "domain";
const upstream_path = "/";
const upstream_mobile = "mobile-domain";
const blocked_region = [];
const blocked_ip_address = ["0.0.0.0", "127.0.0.1"];
const https = true;
const replace_dict = {
  $upstream: "$custom_domain",
  "//domain": "",
  "//mobile-domain": "",
};
addEventListener("fetch", (event) => {
  event.respondWith(fetchAndApply(event.request));
});
async function fetchAndApply(request) {
  const region = request.headers.get("cf-ipcountry").toUpperCase();
  const ip_address = request.headers.get("cf-connecting-ip");
  const user_agent =
    "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.149 Safari/537.36";
  let response = null;
  let url = new URL(request.url);
  let url_hostname = url.hostname;
  if (https == true) {
    url.protocol = "https:";
  } else {
    url.protocol = "http:";
  }
  if (await device_status(user_agent)) {
    var upstream_domain = upstream;
  } else {
    var upstream_domain = upstream_mobile;
  }
  url.host = upstream_domain;
  if (url.pathname == "/") {
    url.pathname = upstream_path;
  } else {
    url.pathname = upstream_path + url.pathname;
  }
  if (blocked_region.includes(region)) {
    response = new Response(
      "Access denied: WorkersProxy is not available in your region yet.",
      {
        status: 403,
      }
    );
  } else if (blocked_ip_address.includes(ip_address)) {
    response = new Response(
      "Access denied: Your IP address is blocked by WorkersProxy.",
      {
        status: 403,
      }
    );
  } else {
    let method = request.method;
    let request_headers = request.headers;
    let new_request_headers = new Headers(request_headers);
    new_request_headers.set("Host", url.hostname);
    new_request_headers.set("Referer", url.hostname);
    let original_response = await fetch(url.href, {
      method: method,
      headers: new_request_headers,
    });
    let original_response_clone = original_response.clone();
    let original_text = null;
    let response_headers = original_response.headers;
    let new_response_headers = new Headers(response_headers);
    let status = original_response.status;
    new_response_headers.set("access-control-allow-origin", "*");
    new_response_headers.set("access-control-allow-credentials", true);
    new_response_headers.delete("content-security-policy");
    new_response_headers.delete("content-security-policy-report-only");
    new_response_headers.delete("clear-site-data");
    const content_type = new_response_headers.get("content-type");
    if (content_type.includes("text/html") && content_type.includes("UTF-8")) {
      original_text = await replace_response_text(
        original_response_clone,
        upstream_domain,
        url_hostname
      );
    } else {
      original_text = original_response_clone.body;
    }
    response = new Response(original_text, {
      status,
      headers: new_response_headers,
    });
  }
  return response;
}
async function replace_response_text(response, upstream_domain, host_name) {
  let text = await response.text();
  var i, j;
  for (i in replace_dict) {
    j = replace_dict[i];
    if (i == "$upstream") {
      i = upstream_domain;
    } else if (i == "$custom_domain") {
      i = host_name;
    }
    if (j == "$upstream") {
      j = upstream_domain;
    } else if (j == "$custom_domain") {
      j = host_name;
    }
    let re = new RegExp(i, "g");
    text = text.replace(re, j);
  }
  return text;
}
async function device_status(user_agent_info) {
  var agents = [
    "Android",
    "iPhone",
    "SymbianOS",
    "Windows Phone",
    "iPad",
    "iPod",
  ];
  var flag = true;
  for (var v = 0; v < agents.length; v++) {
    if (user_agent_info.indexOf(agents[v]) > 0) {
      flag = false;
      break;
    }
  }
  return flag;
}

Change domain and mobile-domain properly, and it will work.