How to fetch certificate string from the certificate store for x509certificate in ASP.NET with C#?

  string samlCertificate = @"-----BEGIN CERTIFICATE-----
BLAHBLAHBLAHBLAHBLAHBLAHBLAHBLAHBLAHBLAHBLAHBLAH123543==
-----END CERTIFICATE-----";

                // 2. Let's read the data - SAML providers usually POST it into the "SAMLResponse" var
                var samlResponse = new Response(samlCertificate, Request.Form["SAMLResponse"]);

                if (samlResponse.IsValid())
                {
                    string username, email, firstname, lastname;

                    username = samlResponse.GetNameID();
                    email = samlResponse.GetEmail();
                    firstname = samlResponse.GetFirstName();
                    lastname = samlResponse.GetLastName();


                }