docs: public static String signSamlResponse(final String samlResponse, final PrivateKey privateKey, final PublicKey publicKey) {
          val doc = constructDocumentFromXml(samlResponse);
  
          if (doc != null) {
              val signedElement = signSamlElement(doc.getRootElement(),
                  privateKey, publicKey);
              doc.setRootElement((org.jdom.Element) signedElement.detach());
              return new XMLOutputter().outputString(doc);
          }
          throw new IllegalArgumentException("Error signing SAML Response: Null document");
      }