protected override void OnPreRequest()
        {
            var postData = new FormPostData();

            postData.AddField("username", Username ?? "");
            postData.AddField("password", Password ?? "");
            (InnerRequest as HttpPostRequest).SetPostData(postData);
        }
        public IEnumerator TestForm()
        {
            var request = new HttpPostRequest("http://httpbin.org/post");

            var data = new FormPostData();

            data.AddBinary("binary", Encoding.UTF8.GetBytes("troll"));
            data.AddField("a1", "a111");
            data.AddField("a2", 22);
            data.AddFile("filez", Encoding.UTF8.GetBytes("content"), "myFile.txt");
            request.SetPostData(data);
            request.Request();

            while (!request.IsFinished)
            {
                yield return(null);
            }

            Debug.Log($"TestForm result:\n{request.Response.TextData}");
        }