docs: private PrivateKey getRSAPrivateKey(Provider provider) {
  
          try {
              RSAPrivateKeySpec privateKeySpec = getRSAPrivateKeySpec();
              KeyFactory factory = provider != null ? KeyFactory.getInstance("RSA", provider)
                      : KeyFactory.getInstance("RSA");
  
              return factory.generatePrivate(privateKeySpec);
          } catch (GeneralSecurityException e) {
              throw new IllegalStateException(e);
          }
      }