code: func getSubjectKeyIdentifierFromCert(cert *x509.Certificate) ([]byte, error) {
  	var SKI []byte
  
  	for _, ext := range cert.Extensions {
  		// Subject Key Identifier is identified by the following ASN.1 tag
  		// subjectKeyIdentifier (2 5 29 14) (see https://tools.ietf.org/html/rfc3280.html)
  		if reflect.DeepEqual(ext.Id, asn1.ObjectIdentifier{2, 5, 29, 14}) {
  			_, err := asn1.Unmarshal(ext.Value, &SKI)
  			if err != nil {
  				return nil, errors.Wrap(err, "failed to unmarshal Subject Key Identifier")
  			}
  
  			return SKI, nil
  		}
  	}
  
  	return nil, errors.New("subjectKeyIdentifier not found in certificate")
  }
docs: // getSubjectKeyIdentifierFromCert returns the Subject Key Identifier for the supplied certificate
  // Subject Key Identifier is an identifier of the public key of this certificate