Rectify (and validate) the given settings using the functions in
    :data:`_settings_rectifiers`.

def _rectify(settings):
    """ Rectify (and validate) the given settings using the functions in
    :data:`_settings_rectifiers`.
    """
    for key, rectifier in _settings_rectifiers.items():
        try:
            new_value = rectifier['func'](settings[key])
            if new_value is False:
                raise AuthzConfigurationError(
                    'Error validating {}->{}: {}'.format(
                        _settings_key, key, rectifier['errmsg']))
            settings[key] = new_value
        except:
            raise AuthzConfigurationError(
                'Error validating {}->{}: {}'.format(
                    _settings_key, key, rectifier['errmsg']))