nginx...

v2

  if ($cors = "simple") {
    set $my_allow_origins "$http_origin";
  }

  if ($cors = "preflight") {
    set $my_allow_origins "$http_origin";
    set $my_allow_methods "GET, HEAD, POST, OPTIONS";
    set $my_allow_headers "Cache-Control";
  }

  location / {
    expires $expires;

    add_header "Access-Control-Allow-Origin" $my_allow_origins;
    add_header "Access-Control-Allow-Methods" $my_allow_methods;
    add_header "Access-Control-Allow-Headers" $my_allow_headers;

    if ($cors = "preflight") {
      return 204;
    }

    try_files $uri /index.html;
  }