How to Extract the Subject DN from an X.509 Certificate in Go?

Extracting the Subject DN from an X.509 Certificate in Go

Problem

Generating a string representation of the subject DN (or issuer DN) from an X.509 certificate in Go can be challenging. The default methods available for the pkix.Name type lack a straightforward way to retrieve this information.

Solution

Using the following custom function, it is possible to convert the certificate's subject or issuer DN into a string:

<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 {
                if name, ok := oid[i.Type.String()]; ok {
                    subject = append(subject, fmt.Sprintf("%s=%s", name, v))
                } else {
                    subject = append(subject, fmt.Sprintf("%s=%s", i.Type.String(), v))
                }
            } else {
                subject = append(subject, fmt.Sprintf("%s=%v", i.Type.String, v))
            }
        }
    }
    return sep + strings.Join(subject, sep), nil
}</code>

Usage

To retrieve the subject DN from a certificate, call the getDNFromCert function as follows:

<code class="go">subj, err := getDNFromCert(x509Cert.Subject, "/")
if err != nil {
   // error handling
}
fmt.Println(subj)</code>

Example Output

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

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