def opt_auth(self, description):
        """
        Specify an authentication method for the server.
        """
        try:
            self.addChecker(makeChecker(description))
        except UnsupportedInterfaces as e:
            raise usage.UsageError(
                'Auth plugin not supported: %s' % e.args[0])
        except InvalidAuthType as e:
            raise usage.UsageError(
                'Auth plugin not recognized: %s' % e.args[0])
        except Exception as e:
            raise usage.UsageError('Unexpected error: %s' % e)

        Specify an authentication method for the server.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/cred/strcred.py