code: public void invoke(X509Certificate cert, GSIConstants.CertificateType certType) throws CertPathValidatorException {
          Set<String> criticalExtensionOids =
                  cert.getCriticalExtensionOIDs();
          if (criticalExtensionOids == null) {
              return;
          }
          for (String criticalExtensionOid : criticalExtensionOids) {
              isUnsupported(certType, criticalExtensionOid);
          }
      }
docs: Method that checks if there are unsupported critical extension. Supported
  ones are only BasicConstrains, KeyUsage, Proxy Certificate (old and new)
  
  @param cert     The certificate to validate.
  @param certType The type of certificate to validate.
  @throws CertPathValidatorException If any critical extension that is not supported is in the certificate.
  Anything other than those listed above will trigger the exception.