code: public boolean validateCrumb(ServletRequest request, MultipartFormDataParser parser) {
          CrumbIssuerDescriptor<CrumbIssuer> desc = getDescriptor();
          String crumbField = desc.getCrumbRequestField();
          String crumbSalt = desc.getCrumbSalt();
  
          return validateCrumb(request, crumbSalt, parser.get(crumbField));
      }
docs: Get a crumb from multipart form data and validate it against other data
  in the current request. The salt and request parameter that is used is
  defined by the current configuration.
  
  @param request
  @param parser