'Gets the authenticated user\'s key specified by id_num.
:param int id_num: (required), unique id of the key
:returns: :class:`Key <github3.users.Key>`'

@requires_auth
def key(self, id_num):

    json = None
    if (int(id_num) > 0):
        url = self._build_url(u'user', u'keys', str(id_num))
        json = self._json(self._get(url), 200)
    return self._instance_or_null(users.Key, json)
