code: def should_add_ClientCertificate(self):
          
          hs_msg = [type(m) for m in self.cur_session.handshake_messages_parsed]
          if TLSCertificateRequest not in hs_msg:
              return
          certs = []
          if self.mycert:
              certs = [self.mycert]
          self.add_msg(TLSCertificate(certs=certs))
          raise self.ADDED_CLIENTCERTIFICATE()
docs: If the server sent a CertificateRequest, we send a Certificate message.
          If no certificate is available, an empty Certificate message is sent:
          - this is a SHOULD in RFC 4346 (Section 7.4.6)
          - this is a MUST in RFC 5246 (Section 7.4.6)
  
          XXX We may want to add a complete chain.