public bool LoginByAutorizationCode(out string result, string url, string clientId = null, string grantType = "authorization_code")
        {
            try
            {
                NameValueCollection queryParams = HttpUtility.ParseQueryString(new UriBuilder(url).Query);
                CODE = queryParams["code"];
                if (string.IsNullOrEmpty(CODE)) CODE = HttpContext.Current.Request.QueryString["code"];
                HttpContext.Current.Session["CODE"] = CODE;

                Dictionary<string, object> fields = new Dictionary<string, object>
                {
                    {"grant_type", grantType},
                    {"client_id", HttpUtility.UrlEncode(CLIENT_ID)},
                    {"client_secret", HttpUtility.UrlEncode(CLIENT_SECRET)},
                    {"redirect_uri", REDIRECT_URI},
                    {"code", CODE}
                };
                KeyValuePair<string, string> authorizations = new KeyValuePair<string, string>
                    ("Authorization", "Bearer " + CODE + "" );
                //Net45
                result = Post(ACCESS_TOKEN_URL, fields).Result;//Send POST and get result

                Dictionary<string, string> headers = new Dictionary<string, string>()
                {
                    { "Bearer", CODE }
                };
                // The response body of this request contains the `access_token` necessary to authenticate your requests
                // Ex : {"access_token": "1234", "token_type": "Bearer", "expires_in": 36000, "refresh_token": "5678", "scope": "read write"}
                // - expires_in => seconds to live for this `access_token`
                // - refresh_token => A token used to fetch a new `access_token` (See below)

                // Now you're all set, the following request shows how to use your `access_token` in your requests
                // If your access token is recognized, this will return information regarding the current user
                //result = Get(USER_URL, null, headers).Result;
                return true;
            }
            catch (Exception ex)
            {
                result = ("[" + new StackTrace(ex, true).GetFrame(0).GetFileLineNumber() + "][" + new StackTrace(ex, true).GetFrame(0).GetMethod().Name + "] " + ex.Message + " => " + ex.InnerException);
                return false;
            }

        }

  public async Task<string> Post(string url, IEnumerable<KeyValuePair<string, object>> parameters, IEnumerable<KeyValuePair<string, string>> headers = null, KeyValuePair<string, string> authorization = default(KeyValuePair<string, string>))
        {
            using (var client = new HttpClient())
            {
                if (!authorization.Equals(default(KeyValuePair<string, string>))) client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(authorization.Key, authorization.Value); //"Bearer", "Your Oauth token"
                if (headers != null) foreach (KeyValuePair<string, string> pair in headers) client.DefaultRequestHeaders.Add(pair.Key, pair.Value);
                using (HttpContent formRequestContent = new FormUrlEncodedContent(parameters.ToDictionary(k => k.Key, k => k.Value?.ToString() ?? "")))
                using (HttpResponseMessage response = await client.PostAsync(url, formRequestContent))
                {

                    //HttpResponseMessage res = await client.PostAsync(url, formRequestContent);
                    //string test = res.Content.ReadAsStringAsync().Result;
                    if (response.IsSuccessStatusCode)
                    {
                        using (HttpContent responseContent = response.Content)
                        {

                            var responseString = await responseContent.ReadAsStringAsync();
                            if (responseString != null) return responseString;
                            return "The POST CALL HAS SUCCEDED BUT RETURN NULL => " + response.RequestMessage;
                        }
                    }
                    else
                    {
                        return "The POST CALL HAS NOT SUCCEDED  => STATUS CODE = " + response.StatusCode;
                    }
                }
            }
        }