If it is possible pass the params through regular GET/POST with a different name and let your server side code handles it.
I had a similar issue with my own proxy to bypass CORS and I got the same error of POST->OPTION in Chrome. It was the Authorization
header in my case ("x-li-format"
and "X-UserName"
here in your case.) I ended up passing it in a dummy format (e.g. AuthorizatinJack
in GET) and I changed the code for my proxy to turn that into a header when making the call to the destination. Here it is in PHP:
if (isset($_GET['AuthorizationJack'])) {
$request_headers[] = "Authorization: Basic ".$_GET['AuthorizationJack'];
}