Get encrypted data from HTTPS request to use certificate manually C#

Question

I am trying for my project this:

1. I want to download the (root) certificate from given url (or from diff location in later stages)
2. i want then get data from given url and use certificate i download in step one to "decrypt them"
3. check response on given url if step 1 and 2 get me same results as just response from the server

Basically I am trying to create something that check that given certificates works on given url same as the one automatically given.

Preferably do all 3 steps in one request (so if given url has counter for access, whole procedure is just one access on website)

I can do quite nice step 1)

var client = new TcpClient(address.ToString(), 443);
var certValidation = new RemoteCertificateValidationCallback(delegate (object snd, X509Certificate certificate, X509Chain chainLocal, SslPolicyErrors sslPolicyErrors)
                {
                    return true; //Accept every certificate, even if it's invalid
                });

// Create an SSL stream and takeover client's stream
using (var sslStream = new SslStream(client.GetStream(), true, certValidation))
{
    sslStream.AuthenticateAsClient(InputWWW.Text);
    var serverCertificate = sslStream.RemoteCertificate;
    cert = new X509Certificate2(serverCertificate);
}

But I am not able to find any tips hot to get that raw data locally.

So far I found only something like this, where I use certificate in request handler

WebRequestHandler handler = new WebRequestHandler();
handler.ClientCertificateOptions = ClientCertificateOption.Manual;
handler.ServerCertificateValidationCallback = (a, b, c, d) => { return true; };
handler.ClientCertificates.Add(certificate);

which is usage of certificate.

I want something like this:

var binary/StringBlob = webRequest.getRawData(url,port);

var serverResponseManualy = applyCertificate/publicKey(binary/StringBlob, X509Certificate2 certificate );

checkBodyEquals(serverResponseManually, webRequest.GetResponse());

Do you know how to do it, or what should I search for?

Is it possible to do all this in one request to server or not?

Thanks