如何使用方法发布使用 HttpRequest 发送变量

首先，检查我试图做的这条消息：

Login
To log on to Windows8 service is through the URL: http://app.proceso.com.mx/win8/login
This URL HTTP Request Method receives POST variables user and pass. The variable user is the user's email and pass the variable is the same password. In the event that the user or password are invalid return plain text number zero 0, in the opposite case, that the username and password are valid return plain text an alphanumeric string of 32 characters, as this b17f27a16589fee247c666da6ed15569, this string is the hash of the valid user valid and will run from 00:00 hours to 23:59 hours the day it was generated.
To test the URL was created: http://app.proceso.com.mx/win8/login_test 
Note: It should be clear that the hash generated will only be valid for Windows8 service to the user that gender and the effect from 00:00 hours to 23:59 on the day it was generated.
Note: All services generate text in UTF-8

下面是一个测试帐户：

• 用户： javier.lopez.contreras10@gmail.com
• 通行证：波利卡皮奥20

因此，如果您在此页面中设置数据：http://app.proceso.com.mx/win8/login_test 您将收到一个哈希代码。

这就是我在地铁应用程序中试图实现的目标，但我感到迷茫。我不知道发送这些数据来接收哈希代码。我正在使用HttpClient和HttpContent，但我不确定。

提前谢谢。

更新：感谢dharnitski的代码，现在我正在为Win8 CP修改此代码：

        // this is what we are sending
        string post_data = "user=javier.lopez.contreras10@gmail.com&pass=policarpio20";
        // this is where we will send it
        string uri = "http://app.proceso.com.mx/win8/login";
        // create a request
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
        request.Method = "POST";
        // turn our request string into a byte stream
        byte[] postBytes = Encoding.UTF8.GetBytes(post_data);
        // this is important - make sure you specify type this way
        request.ContentType = "application/x-www-form-urlencoded";
        Stream requestStream = await request.GetRequestStreamAsync();
        // now send it
        requestStream.Write(postBytes, 0, postBytes.Length);
        // grab te response and print it out to the console along with the status code
        WebResponse response = await request.GetResponseAsync();
        //var a = new StreamReader(response.GetResponseStream()).ReadToEnd();
        StreamReader requestReader = new StreamReader(response.GetResponseStream());
        String webResponse = requestReader.ReadToEnd();

我意识到，HttpWebRequest 不包含 ProtocolVersion，并且在此行中向我抛出此错误：

WebResponse response = await request.GetResponseAsync();
// ERROR: The remote server returned an error: (417) Expectation Failed.

如果我可以修改协议版本，如何解决此问题？