The IRequest::get_ClientCertificate method retrieves the ClientCertificate collection of the Request object.
HRESULT get_ClientCertificate(
  IRequestDictionary ** ppDictReturn  //pointer to an 
                                      // IRequestDictionary interface
                                      // pointer that receives the
                                      // ClientCertificate collection
);
 You can iterate through the ClientCertificate collection with the get__NewEnum method exposed by the IRequestDictionary interface. You can also retrieve a specific ClientCertificate value with the get_Item method.