如何使用UploadStringAsync C＃传递正文数据

Question

我尝试使用WebClient类在POST请求的正文中传递一个字符串。以下是我的代码：

protected void GetAccessToken(string client_id, string secret)
    {
        var urlEncodedSecret = HttpUtility.UrlEncode(secret);
        var urlEncodedSid = HttpUtility.UrlEncode(client_id);

        string bodyData = String.Format("grant_type=client_credentials&client_id=ms-app%3a%2f%2f{0}&client_secret={1}&scope=notify.windows.com", client_id, secret);

        string address = "https://login.live.com/accesstoken.srf";
        string myParameters = "param1=value1&param2=value2&param3=value3";

        Uri URI = new Uri(address);
        System.Net.WebClient webClient = new WebClient();
        webClient.BaseAddress = address;

        webClient.Headers["Content-Type"] = "application/x-www-form-urlencoded";
        webClient.Headers["Content-Length"] = "211";
        webClient.Headers["Host"] = "https://login.live.com";

        webClient.UploadStringCompleted += new UploadStringCompletedEventHandler(uploadStringCompleted);
        webClient.UploadStringAsync(URI, "POST", bodyData);
    }

    private void uploadStringCompleted(object sender, UploadStringCompletedEventArgs e)
    {
        string json = e.Result.ToString();
        _oAuthToken = GetOAuthTokenFromJson(json);
    }

当我运行应用程序时，我收到异常＆＃34;远程服务器返回错误：NotFound。＆＃34;。 我使用邮递员成功地提出了同样的要求：

任何人都知道我的要求有问题吗？或者是让我走上正确道路的东西！？