class Crypto {

    public static String extractX509CSRSubjectField(PKCS10CertificationRequest certReq, ASN1ObjectIdentifier id) {

        X500Name x500name = certReq.getSubject();
        if (x500name == null) {
            return null;
        }
        RDN[] rdns = x500name.getRDNs(id);

        // we're only supporting a single field in Athenz certificates so
        // any other multiple value will be considered invalid

        if (rdns == null || rdns.length == 0) {
            return null;
        }

        if (rdns.length != 1) {
            throw new CryptoException("CSR Subject contains multiple values for the same field.");
        }

        return IETFUtils.valueToString(rdns[0].getFirst().getValue());
    }

}