code: public Map<String, String> parseParameters(HttpServletRequest request) {
      Map<String, String> parameters = parseHeaderParameters(request);
  
      if (parameters == null) {
        //if there is no header authorization parameters, then the oauth parameters are the supported OAuth request parameters.
        parameters = new HashMap<String, String>();
        for (String supportedOAuthParameter : getSupportedOAuthParameters()) {
          String param = request.getParameter(supportedOAuthParameter);
          if (param != null) {
            parameters.put(supportedOAuthParameter, param);
          }
        }
      }
  
      return parameters;
    }
docs: Inherited.