/**
   * Add a given extension field for the standard extensions tag (tag 3) copying the extension value
   * from another certificate.
   *
   * @param oid the OID defining the extension type.
   * @param isCritical true if the copied extension is to be marked as critical, false otherwise.
   * @param certHolder the holder for the certificate that the extension is to be copied from.
   * @return this builder object.
   */
  public X509v3CertificateBuilder copyAndAddExtension(
      ASN1ObjectIdentifier oid, boolean isCritical, X509CertificateHolder certHolder) {
    X509CertificateStructure cert = certHolder.toASN1Structure();

    X509Extension extension = cert.getTBSCertificate().getExtensions().getExtension(oid);

    if (extension == null) {
      throw new NullPointerException("extension " + oid + " not present");
    }

    extGenerator.addExtension(oid, isCritical, extension.getValue().getOctets());

    return this;
  }
  /**
   * Add a given extension field for the standard extensions tag (tag 3)
   *
   * @param oid the OID defining the extension type.
   * @param isCritical true if the extension is critical, false otherwise.
   * @param value the ASN.1 structure that forms the extension's value.
   * @return this builder object.
   */
  public X509v3CertificateBuilder addExtension(
      ASN1ObjectIdentifier oid, boolean isCritical, ASN1Encodable value) {
    extGenerator.addExtension(oid, isCritical, value);

    return this;
  }