建立和傳送 HTTP POST 請求

using System.Net;
using System.IO;

...

string requestUrl = "https://www.example.com/submit.html";
HttpWebRequest request = HttpWebRequest.CreateHttp(requestUrl);
request.Method = "POST";

// Optionally, set properties of the HttpWebRequest, such as:
request.AutomaticDecompression = DecompressionMethods.Deflate | DecompressionMethods.GZip;
request.ContentType = "application/x-www-form-urlencoded";
// Could also set other HTTP headers such as Request.UserAgent, Request.Referer,
// Request.Accept, or other headers via the Request.Headers collection.

// Set the POST request body data. In this example, the POST data is in 
// application/x-www-form-urlencoded format.
string postData = "myparam1=myvalue1&myparam2=myvalue2";
using (var writer = new StreamWriter(request.GetRequestStream()))
{
    writer.Write(postData);
}

// Submit the request, and get the response body from the remote server.
string responseFromRemoteServer;
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
    using (StreamReader reader = new StreamReader(response.GetResponseStream()))
    {
        responseFromRemoteServer = reader.ReadToEnd();
    }
}