'Counts how many of the keys that identify a single application
as having a fig-format are found in the supplied application
definition.
:param dict config: A single application definition from
the application_configuration dictionary.
:returns: ``int`` representing the number of identifying keys found.'

def _count_identifier_keys(self, config):

    config_keys = set(config)
    return len((self._possible_identifiers & config_keys))
