Relative Distinguish Name to string

rdns2str.go

var (
	cnNameOid = asn1.ObjectIdentifier{2, 5, 4, 3}
	emailOid  = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 9, 1}
	userIDOid = asn1.ObjectIdentifier{0, 9, 2342, 19200300, 100, 1, 1}
	dcNameOid = asn1.ObjectIdentifier{0, 9, 2342, 19200300, 100, 1, 25}
)

// RDNSToString returns the Relative Distinguish Name as a string.
func RDNSToString(rdns *pkix.RDNSequence) string {
	var buf strings.Builder
	for _, rdn := range *rdns {
		if len(rdn) == 0 {
			continue
		}
		for _, atv := range rdn {
			value, ok := atv.Value.(string)
			if !ok {
				continue
			}
			t := atv.Type
			if len(t) == 4 && t[0] == 2 && t[1] == 5 && t[2] == 4 {
				switch t[3] {
				case 3:
					buf.WriteString("/CN=") // common name
					buf.WriteString(value)
				case 4:
					buf.WriteString("/SN=") // surname
					buf.WriteString(value)
				case 5:
					buf.WriteString("/SERIALNUMBER=")
					buf.WriteString(value)
				case 6:
					buf.WriteString("/C=") // country
					buf.WriteString(value)
				case 7:
					buf.WriteString("/L=") // locality
					buf.WriteString(value)
				case 8:
					buf.WriteString("/ST=") // state
					buf.WriteString(value)
				case 9:
					buf.WriteString("/STREET=")
					buf.WriteString(value)
				case 10:
					buf.WriteString("/O=") // organization
					buf.WriteString(value)
				case 11:
					buf.WriteString("/OU=") // organization unit
					buf.WriteString(value)
				case 12:
					buf.WriteString("/T=") // title
					buf.WriteString(value)
				case 17:
					buf.WriteString("/PC=") // postal code
					buf.WriteString(value)
				case 42:
					buf.WriteString("/GN=") // given name
					buf.WriteString(value)
				case 43:
					buf.WriteString("/initials=")
					buf.WriteString(value)
				case 44:
					buf.WriteString("/generationQualifier=")
					buf.WriteString(value)
				case 46:
					buf.WriteString("/dnQualifier=")
					buf.WriteString(value)
				case 65:
					buf.WriteString("/pseudonym=")
					buf.WriteString(value)
				}
			} else if t.Equal(dcNameOid) {
				buf.WriteString("/DC=") // domain component
				buf.WriteString(value)
			} else if t.Equal(emailOid) {
				buf.WriteString("/MAIL=")
				buf.WriteString(value)
			} else if t.Equal(userIDOid) {
				buf.WriteString("/UID=") // user ID
				buf.WriteString(value)
			}
		}
	}
	return buf.String()
}

func main() {
	
	...
	cert, err := x509.ParseCertificate(certData)
	if err != nil {
	    ...
	}

	var rdns pkix.RDNSequence
	if _, err := asn1.Unmarshal(cert.RawSubject, &rdns); err != nil {
	    ...
	}

	fmt.Println("Subject:", RDNSToString(&rdns))
	...
}