How to send a client certificate by using the HttpWebRequest and HttpWebResponse classes in Microsoft Visual C# .NET | ASP.NET HttpWebRequest Tutorial Advanced | Scoop.it

You can send a client certificate when the Web server requires one by using the HttpWebRequest and the HttpWebResponse classes. To obtain a certificate that can be used for sending a client certificate by using the HttpWebRequest class, use one of the following methods:
Method 1

Use the X509Certificate class to read the certificate from a .cer file, and then set the ClientCertificates property.
Method 2

Use CryptoAPI calls to obtain the certificate from the certificate store, and then set the X509Certificate class to the certificate that you received from the certificate store. You can then set the ClientCertificates property.

 

http://www.kerrywong.com/2006/12/01/using-x509-certificate-with-web-service-in-aspnet/