private static Optional<X509Certificate> extractCertificate(final Object[] certs) {
        for (final Object cert : certs) {
            if (cert instanceof X509Certificate) {
                return Optional.of((X509Certificate) cert);
            }
        }
        return Optional.empty();
    }
Pull out the Subject from the certificate. E.g.
"CN=some.server.co.uk, OU=servers, O=some organisation, C=GB"

@param certs ARGS from the SERVLET request.
stroom-receive/stroom-receive-common/src/main/java/stroom/receive/common/CertificateExtractorImpl.java