How to Extract the Complete Subject or Issuer DN from an X509 Certificate in Go?

Retrieve Complete Subject or Issuer DN from X509 Certificate in Go

Retrieving the complete subject or issuer Distinguished Name (DN) from an X509 certificate as a string can be accomplished using a few steps.

Solution Details:

1. Map OIDs to Attribute Names:

   • Create a map to associate OIDs (Object Identifiers) to attribute names.

2. Convert RDNSequence to String:

   • Convert the RDNSequence (Relative Distinguished Name Sequence) to a slice of strings, where each string represents an attribute (e.g., "CN=common name").

3. Build Subject DN String:

   • Iterate over the slice of strings and build the subject DN string by concatenating the attribute names and values.

4. Call the Function:

   • Invoke the getDNFromCert function with the certificate subject or issuer as an argument.

Example Usage:

<code class="go">func main() {
    // Obtain the X509 certificate
    x509Cert, err := LoadCert(pemBytes)
    if err != nil {
        // Handle error
    }

    // Retrieve subject DN
    subj, err := getDNFromCert(x509Cert.Subject, "/")
    if err != nil {
        // Handle error
    }

    fmt.Println("Subject DN:", subj)
}</code>

Function Definition:

<code class="go">func getDNFromCert(namespace pkix.Name, sep string) (string, error) {
    subject := []string{}
    for _, s := range namespace.ToRDNSequence() {
        for _, i := range s {
            if v, ok := i.Value.(string); ok {
                subject = append(subject, fmt.Sprintf("%v=%v", i.Type.String(), v))
            } else {
                subject = append(subject, fmt.Sprintf("%v=%v", i.Type.String(), i.Value))
            }
        }
    }
    return sep + strings.Join(subject, sep), nil
}</code>

Expected Output:

Subject DN: /C=US/O=some organization/OU=unit/CN=common name

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