code: protected void collectBodyParameters(HttpRequest request, HttpParameters out)
              throws IOException {
  
          // collect x-www-form-urlencoded body params
          String contentType = request.getContentType();
          if (contentType != null && contentType.startsWith(OAuth.FORM_ENCODED)) {
              InputStream payload = request.getMessagePayload();
              out.putAll(OAuth.decodeForm(payload), true);
          }
      }
docs: Collects x-www-form-urlencoded body parameters as per OAuth Core 1.0 spec
  section 9.1.1