code: def is_certificate_valid(stream, cert):
          
          try:
              logger.debug("tls_is_certificate_valid(cert = {0!r})".format(cert))
              if not cert:
                  logger.warning("No TLS certificate information received.")
                  return False
              if not cert.validated:
                  logger.warning("TLS certificate not validated.")
                  return False
              srv_type = stream.transport._dst_service # pylint: disable=W0212
              if cert.verify_server(stream.peer, srv_type):
                  logger.debug(" tls: certificate valid for {0!r}"
                                                          .format(stream.peer))
                  return True
              else:
                  logger.debug(" tls: certificate not valid for {0!r}"
                                                          .format(stream.peer))
                  return False
          except:
              logger.exception("Exception caught while checking a certificate")
              raise
docs: Default certificate verification callback for TLS connections.
  
          :Parameters:
              - `cert`: certificate information
          :Types:
              - `cert`: `CertificateData`
  
          :return: computed verification result.