Related: how-do-i-use-webrequest-to-access-an-ssl-encrypted-site-using-https
How to send an HTTPS GET Request in C#?
Add ?var1=data1&var2=data2
to the end of url to submit values to the page via GET:
using System.Net;
using System.IO;
string url = "https://www.example.com/scriptname.php?var1=hello";
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
Stream resStream = response.GetResponseStream();