docs: def get_user_of_group(config, fas, groupname):
      ''' Return the list of users in the specified group.
  
      :arg config: a dict containing the fedmsg config
      :arg fas: a fedora.client.fas2.AccountSystem object instanciated and loged
          into FAS.
      :arg groupname: the name of the group for which we want to retrieve the
          members.
      :return: a list of FAS user members of the specified group.
      '''
  
      if not _cache.is_configured:
          _cache.configure(**config['fmn.rules.cache'])
  
      key = cache_key_generator(get_user_of_group, groupname)
      def creator():
          if not fas:
              return set()
          return set([u.username for u in fas.group_members(groupname)])
      return _cache.get_or_create(key, creator)