'Stores session information in the cache. Assumes that the subject_id
is unique within the context of the Service Provider.
:param subject_id: The subject identifier
:param entity_id: The identifier of the entity_id/receiver of an
assertion
:param info: The session info, the assertion is part of this
:param timestamp: A time after which the assertion is not valid.'

def set(self, subject_id, entity_id, info, timestamp=0):

    if (isinstance(timestamp, datetime) or isinstance(timestamp, time.struct_time)):
        timestamp = time.strftime(TIME_FORMAT, timestamp)
    doc = {'subject_id': subject_id, 'entity_id': entity_id, 'info': info, 'timestamp': timestamp}
    _ = self._cache.insert(doc)
