c# - get ssl certificate in .net

Question

i am looking to get the data from any given domain names SSL certificate. For example I want to put in any website address e.g. "http://stackoverflow.com" and my code would firstly check if an SSL certificate exists. If it does then I want it to pull out the expiry date of the certificate. [ i am reading Domainnames from DB ] Example :http://www.digicert.com/help/

i need to create a web service to check expiry date. how can i implement it?? - I have looked up loads of different things such as RequestCertificateValidationCallback and ClientCertificates etc.

I could be completely wrong (hence why I need help) but would I create a HTTPWebRequest and then somehow request the client certificate and specific elements that way?

i tried the example provided @SSL certificate pre-fetch .NET , but i am getting forbitten 403 error.

Answer 1

For this to work your project will need a reference to System.Security:

using System.Security;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;

//Do webrequest to get info on secure site
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://mail.google.com");
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
response.Close();

//retrieve the ssl cert and assign it to an X509Certificate object
X509Certificate cert = request.ServicePoint.Certificate;

//convert the X509Certificate to an X509Certificate2 object by passing it into the constructor
X509Certificate2 cert2 = new X509Certificate2(cert);

string cn = cert2.GetIssuerName();
string cedate = cert2.GetExpirationDateString();
string cpub = cert2.GetPublicKeyString();

//display the cert dialog box
X509Certificate2UI.DisplayCertificate(cert2);

.Net Core 2.1

You can use HttpClientHandler and ServerCertificateCustomValidationCallback Property. (This class is available in .net 4.7.1 and above also).

var handler = new HttpClientHandler
{
     UseDefaultCredentials = true,

     ServerCertificateCustomValidationCallback = (sender, cert, chain, error) =>
     {

          /// Access cert object.

          return true;
     }
 };

 using (HttpClient client = new HttpClient(handler))
 {
     using (HttpResponseMessage response = await client.GetAsync("https://mail.google.com"))
     {
          using (HttpContent content = response.Content)
          {

          }
      }
 }