[OperationContract]
    [WebInvoke(Method = "POST", ResponseFormat = WebMessageFormat.Json, BodyStyle = WebMessageBodyStyle.Wrapped,
        UriTemplate = "{id}/{spec}/Enroll/Commit/{serverSessionID}?callbackID={callbackID}")]
    Stream IssueTokensCommit(string id, string spec, string serverSessionID, string callbackID);

 // implementation of above interface - Doesn't work
  // StreamReader reader = new StreamReader(HttpContext.Current.Request.InputStream);
 // string secondMessageFromProver = reader.ReadToEnd();