code: func (s *LocalStore) GetHTTPChallengeToken(token, domain string) ([]byte, error) {
  	s.lock.RLock()
  	defer s.lock.RUnlock()
  
  	if s.storedData.HTTPChallenges == nil {
  		s.storedData.HTTPChallenges = map[string]map[string][]byte{}
  	}
  
  	if _, ok := s.storedData.HTTPChallenges[token]; !ok {
  		return nil, fmt.Errorf("cannot find challenge for token %v", token)
  	}
  
  	result, ok := s.storedData.HTTPChallenges[token][domain]
  	if !ok {
  		return nil, fmt.Errorf("cannot find challenge for token %v", token)
  	}
  	return result, nil
  }
docs: // GetHTTPChallengeToken Get the http challenge token from the store