Using WWW class in WebGL to send POST data with custom headers

Edit: I appear to have figured out how to post the data, but the content-type is x-www-form-urlencoded and the server only supports application/json. Is there a way to do this with Unity and WebGL?


I'm trying to use a RESTFUL API and send POST data to our server. Here is what I am trying and the POST data is appearing empty on the server side.

Here is the cURL request I am trying to make
curl -X POST \
-H "CUSTOM HEADER: MyHeader" \
-H "CUSTOM HEADER2: MyHeader2" \
-H "Content-Type: application/json" \
-d '{"unitykeytest":"unitykeyvalue"}' \
https://mywebserver/my/restful/api


[Attempting: POST request - custom headers - POST data]

var header = new Dictionary<string, string>();

header.Add("CUSTOM HEADER", MyHeader1);
header.Add("CUSTOM HEADER2", MyHeader2);
header.Add("Content-Type", "application/json");

string json = "{ \"unitykeytest\": \"unitykeyvalue\"}";
string url = "http://mywebserver/test/requestTest.php";
WWW www;
var encoding = new System.Text.ASCIIEncoding();
www = new WWW(url, encoding.GetBytes(json), header);

yield return www;

// Handle www request

On the server side, I am getting an empty $_POST variable
Array
(
)

with everything else looking correct.
I have tried RESTSharp and other libraries for c# but they all use Async and will not work on WebGL.

Thank you