code: protected static String getElement(JWTPayload payload, String element) {
          String output = null;
          if (payload != null) {
              Object outObj = payload.get(element);
              if (outObj instanceof String) {
                  output = (String) outObj;
              } else if (outObj instanceof List) {
                  if (((List<String>) outObj).size() == 1) {
                      output = ((List<String>) outObj).get(0);
                  }
                  // if there are multiple values, return null.
              }
          }
          return output;
      }
docs: Get Aud element.