@Override
    protected String resolvePrincipalInternal(final X509Certificate certificate) {
        val principal = certificate.getSerialNumber().toString(radix);
        if (zeroPadding && principal.length() % 2 != 0) {
            return '0' + principal;
        }
        return principal;
    }
Returns a new principal based on the serial number of the certificate.

@author Scott Battaglia
@since 3.0.0
support/cas-server-support-x509-core/src/main/java/org/apereo/cas/adaptors/x509/authentication/principal/X509SerialNumberPrincipalResolver.java