Bind, use tls

def _open(self):
        """Bind, use tls"""
        try:
            self.ldap.start_tls_s()
        #pylint: disable=no-member
        except ldap.CONNECT_ERROR:
        #pylint: enable=no-member
            logging.error('Unable to establish a connection to the LDAP server, ' + \
                          'please check the connection string ' + \
                          'and ensure the remote certificate is signed by a trusted authority.')
            raise

        self.ldap.simple_bind_s(self.user, self.password)