Custom Auth HTTPS POST

How do you send data VIA POST instead of GET?

What is the format?

I tried the following but it doesn't work

string _postData = "{'test':'123'}";
byte[] postData = System.Text.Encoding.UTF8.GetBytes (_postData);
PhotonNetwork.AuthValues.SetAuthPostData (postData);

string postData = "{'test':'123'}";
PhotonNetwork.AuthValues.SetAuthPostData (postData);