C# – Why does My HTTP Web Request Code Not Send a Request

You are creating a new CookieContainer each time. Try using the CookieContainer of the index page request as the container for the form submit, it should contain the extra cookie. Alternatively, something other than the form could be passing the extra cookie. Check when the page loads using IEinspector's HttpAnalyzer or Firefox's Firebug to make sure other form elements like images aren't passing the cookie.

There are several ways to perform HTTP GET and POST requests:

Method A: HttpClient (Preferred)

Available in: .NET Framework 4.5+, .NET Standard 1.1+, .NET Core 1.0+ .

It is currently the preferred approach, and is asynchronous and high performance. Use the built-in version in most cases, but for very old platforms there is a NuGet package.

using System.Net.Http;

Setup

It is recommended to instantiate one HttpClient for your application's lifetime and share it unless you have a specific reason not to.

private static readonly HttpClient client = new HttpClient();

See HttpClientFactory for a dependency injection solution.

• POST

  var values = new Dictionary<string, string>
  {
      { "thing1", "hello" },
      { "thing2", "world" }
  };
  
  var content = new FormUrlEncodedContent(values);
  
  var response = await client.PostAsync("http://www.example.com/recepticle.aspx", content);
  
  var responseString = await response.Content.ReadAsStringAsync();
  

• GET

  var responseString = await client.GetStringAsync("http://www.example.com/recepticle.aspx");
  

Method B: Third-Party Libraries

RestSharp

• POST

   var client = new RestClient("http://example.com");
   // client.Authenticator = new HttpBasicAuthenticator(username, password);
   var request = new RestRequest("resource/{id}");
   request.AddParameter("thing1", "Hello");
   request.AddParameter("thing2", "world");
   request.AddHeader("header", "value");
   request.AddFile("file", path);
   var response = client.Post(request);
   var content = response.Content; // Raw content as string
   var response2 = client.Post<Person>(request);
   var name = response2.Data.Name;
  

Flurl.Http

It is a newer library sporting a fluent API, testing helpers, uses HttpClient under the hood, and is portable. It is available via NuGet.

    using Flurl.Http;

• POST

  var responseString = await "http://www.example.com/recepticle.aspx"
      .PostUrlEncodedAsync(new { thing1 = "hello", thing2 = "world" })
      .ReceiveString();
  

• GET

  var responseString = await "http://www.example.com/recepticle.aspx"
      .GetStringAsync();
  

Method C: HttpWebRequest (not recommended for new work)

Available in: .NET Framework 1.1+, .NET Standard 2.0+, .NET Core 1.0+. In .NET Core, it is mostly for compatibility -- it wraps HttpClient, is less performant, and won't get new features.

using System.Net;
using System.Text;  // For class Encoding
using System.IO;    // For StreamReader

• POST

  var request = (HttpWebRequest)WebRequest.Create("http://www.example.com/recepticle.aspx");
  
  var postData = "thing1=" + Uri.EscapeDataString("hello");
      postData += "&thing2=" + Uri.EscapeDataString("world");
  var data = Encoding.ASCII.GetBytes(postData);
  
  request.Method = "POST";
  request.ContentType = "application/x-www-form-urlencoded";
  request.ContentLength = data.Length;
  
  using (var stream = request.GetRequestStream())
  {
      stream.Write(data, 0, data.Length);
  }
  
  var response = (HttpWebResponse)request.GetResponse();
  
  var responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();
  

• GET

  var request = (HttpWebRequest)WebRequest.Create("http://www.example.com/recepticle.aspx");
  
  var response = (HttpWebResponse)request.GetResponse();
  
  var responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();
  

Method D: WebClient (Not recommended for new work)

This is a wrapper around HttpWebRequest. Compare with HttpClient.

Available in: .NET Framework 1.1+, NET Standard 2.0+, .NET Core 2.0+

using System.Net;
using System.Collections.Specialized;

• POST

  using (var client = new WebClient())
  {
      var values = new NameValueCollection();
      values["thing1"] = "hello";
      values["thing2"] = "world";
  
      var response = client.UploadValues("http://www.example.com/recepticle.aspx", values);
  
      var responseString = Encoding.Default.GetString(response);
  }
  

• GET

  using (var client = new WebClient())
  {
      var responseString = client.DownloadString("http://www.example.com/recepticle.aspx");
  }