Go: get value of 'subject/unstructeredName' from a ssl certificate - go

Question

I'm trying to migrate some python code to golang.
The code needs to get the value of unstructuredName from the ssl certificates subject.
Here is how it works in python:
from cryptography import x509
from cryptography.x509.oid import NameOID
from cryptography.hazmat.backends import default_backend
pem = b"""\
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
"""
cert = x509.load_pem_x509_certificate(pem, default_backend())
unstructured_name = cert.subject.get_attributes_for_oid(NameOID.UNSTRUCTURED_NAME)[0].value
print(unstructured_name)
This code prints the value ("some additional info" in this case) of unstructuredName.
My attempt in go looks like this:
package main
import (
"crypto/x509"
"encoding/pem"
"fmt"
"log"
)
const certRaw = `-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
`
func main() {
block, rest := pem.Decode([]byte(certRaw))
if block == nil {
log.Fatalf("Decode CA PEM, %v", rest)
}
cert, err := x509.ParseCertificate(block.Bytes)
if err != nil {
log.Fatalf("parse certificate")
}
fmt.Println(cert.Subject.String())
// Unmarshall and print value of unstructuredName (oid: 1.2.840.113549.1.9.2)
// ???
}
Go Playground: https://go.dev/play/p/VwkpDbNpQ78
I couldn't find a function to get the attribute by oid. When I print out the whole subject I see that the value is still (DER?) encoded.
How can I decode or unmarshal the value of the unstructuredName?
Thanks a lot.

Answer 1

I don't think the Go standard lib has a function to get the attribute by the oid. However, it doesn't look like it's very hard to write one yourself. The code below is based on this related answer (and the code in your question).
Here's the updated go playground - https://go.dev/play/p/NtfZ6Kl_Vl0.
package main
import (
"crypto/x509"
"encoding/pem"
"fmt"
"log"
)
const certRaw = `-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
`
func main() {
block, rest := pem.Decode([]byte(certRaw))
if block == nil {
log.Fatalf("Decode CA PEM, %v", rest)
}
cert, err := x509.ParseCertificate(block.Bytes)
if err != nil {
log.Fatalf("parse certificate")
}
// 1.2.840.113549.1.9.2
var oidUnstructuredName = []int{1, 2, 840, 113549, 1, 9, 2}
var unstructuredName string
for _, n := range cert.Subject.Names {
if n.Type.Equal(oidUnstructuredName) {
if v, ok := n.Value.(string); ok {
unstructuredName = v
}
}
}
fmt.Println(unstructuredName)
}