docs: private static PrivateKey getPrivateKey(String filename, String password, String key) {
          if(logger.isDebugEnabled()) logger.debug("filename = " + filename + " key = " + key);
          PrivateKey privateKey = null;
  
          try {
              KeyStore keystore = KeyStore.getInstance("JKS");
              keystore.load(Config.getInstance().getInputStreamFromFile(filename),
                      password.toCharArray());
  
              privateKey = (PrivateKey) keystore.getKey(key,
                      password.toCharArray());
          } catch (Exception e) {
              logger.error("Exception:", e);
          }
  
          if (privateKey == null) {
              logger.error("Failed to retrieve private key from keystore");
          }
  
          return privateKey;
      }