def _checkerFactoriesForOptHelpAuth(self):
        """
        Return a list of which authTypes will be displayed by --help-auth.
        This makes it a lot easier to test this module.
        """
        for factory in findCheckerFactories():
            for interface in factory.credentialInterfaces:
                if self.supportsInterface(interface):
                    yield factory
                    break

        Return a list of which authTypes will be displayed by --help-auth.
        This makes it a lot easier to test this module.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/cred/strcred.py