X509ExampleBus.cs

public IRegistryService Connect(String name, RSACryptoServiceProvider privateKey, X509Certificate2 acsCertificate) {
  if ((String.IsNullOrEmpty(name)) || (acsCertificate == null) ||
      (privateKey == null))
    throw new ArgumentException("....");

  if (!String.IsNullOrEmpty(this.Credential.identifier))
    throw new ACSLoginFailureException("....");

  byte[] challenge = this.acs.getChallenge(name);      
  byte[] answer = new byte[0];
  try {
    answer = Crypto.GenerateAnswer(challenge, privateKey, acsCertificate);
  }
  catch (CryptographicException e) {
    throw new ACSLoginFailureException("....", e);
  }

  bool connect = this.acs.loginByCertificate(name, answer, out this.credential, out leaseTime);      

  // ...
}