code: func keyUsageString(ku x509.KeyUsage) string {
  	switch ku {
  	case x509.KeyUsageDigitalSignature:
  		return "DigitalSignature"
  	case x509.KeyUsageContentCommitment:
  		return "ContentCommitment"
  	case x509.KeyUsageKeyEncipherment:
  		return "KeyEncipherment"
  	case x509.KeyUsageDataEncipherment:
  		return "DataEncipherment"
  	case x509.KeyUsageKeyAgreement:
  		return "KeyAgreement"
  	case x509.KeyUsageCertSign:
  		return "CertSign"
  	case x509.KeyUsageCRLSign:
  		return "CRLSign"
  	case x509.KeyUsageEncipherOnly:
  		return "EncipherOnly"
  	case x509.KeyUsageDecipherOnly:
  		return "DecipherOnly"
  	}
  	return "Unknown"
  }
docs: // keyUsageString returns the name of the keyusage as string