code: func ValidChallenge(name string) bool {
  	switch name {
  	case ChallengeTypeHTTP01,
  		ChallengeTypeDNS01,
  		ChallengeTypeTLSALPN01:
  		return true
  	default:
  		return false
  	}
  }
docs: // ValidChallenge tests whether the provided string names a known challenge