code: func (s Session) SessionTimeoutExpiredOrMissing() bool {
  	if exp, present := s[TimestampKey]; !present {
  		return true
  	} else if exp == SessionValueName {
  		return false
  	} else if expInt, _ := strconv.Atoi(exp.(string)); int64(expInt) < time.Now().Unix() {
  		return true
  	}
  	return false
  }
docs: // sessionTimeoutExpiredOrMissing returns a boolean of whether the session
  // cookie is either not present or present but beyond its time to live; i.e.,
  // whether there is not a valid session.