绕过登录并从URL下载Zip文件

Question

I want to download a zip file form URL.It contains 20 to 30 CSV file and has total size between 50 KB to 100 KB. I have tried using below code but it is not working. When i directly open URL from web browser it redirects to login page and after successful login download the zip file.

  using (var client = new WebClient())
  {
    client.DownloadFile("http://MyURL","Myfile.zip");
  }

If i provide Download URL of CSV file in above code then it download html login page. Also tried by providing credential and header information as below but it is not working.

    using (var client = new WebClient())
      {
         client.Credentials = new NetworkCredential("username", "password");
         client.Headers.Add(HttpRequestHeader.AcceptEncoding, "gzip");
         client.DownloadFile("http://MyURL","Myfile.zip");
      }    

I am using C# windows application.