code: func (tm *tokenManager) clear() {
  	for _ = range time.Tick(time.Minute * 3) {
  		keys := make([]interface{}, 0, 100)
  
  		for item := range tm.Iter() {
  			if time.Now().Sub(item.val.(token).createTime) > tm.expiredAfter {
  				keys = append(keys, item.key)
  			}
  		}
  
  		tm.DeleteMulti(keys)
  	}
  }
docs: // clear removes expired tokens.