key_cacher.go
func (mkc *memoryKeyCacher) keyIsExpired(keyID string) bool {
	if time.Now().After(mkc.entries[keyID].addedAt.Add(mkc.maxKeyAge)) {
		delete(mkc.entries, keyID)
		return true
	}
	return false
}
func (mkc *memoryKeyCacher) keyIsExpired(keyID string) bool {
	if time.Now().After(mkc.entries[keyID].addedAt.Add(mkc.maxKeyAge)) {
		delete(mkc.entries, keyID)
		return true
	}
	return false
}
// keyIsExpired deletes the key from cache if it is expired