    def check_allow_config(self):
        """Log a warning if no allow config can be found.

        Could get a false positive if _only_ unrecognized allow config is used.
        Authenticators can apply `.tag(allow_config=True)` to label this config
        to make sure it is found.

        Subclasses can override to perform additonal checks and warn about likely
        authenticator configuration problems.

        .. versionadded:: 5.0
        """
        if not self.any_allow_config:
            self.log.warning(
                "No allow config found, it's possible that nobody can login to your Hub!\n"
                "You can set `c.Authenticator.allow_all = True` to allow any user who can login to access the Hub,\n"
                "or e.g. `allowed_users` to a set of users who should have access.\n"
                "You may suppress this warning by setting c.Authenticator.any_allow_config = True."
            )
Log a warning if no allow config can be found.

Could get a false positive if _only_ unrecognized allow config is used.
Authenticators can apply `.tag(allow_config=True)` to label this config
to make sure it is found.

Subclasses can override to perform additonal checks and warn about likely
authenticator configuration problems.

.. versionadded:: 5.0
jupyterhub/auth.py