code: @Override
      public boolean validateCrumb(ServletRequest request, String salt, String crumb) {
          if (request instanceof HttpServletRequest) {
              String newCrumb = issueCrumb(request, salt);
              if ((newCrumb != null) && (crumb != null)) {
                  // String.equals() is not constant-time, but this is
                  return MessageDigest.isEqual(newCrumb.getBytes(Charset.forName("US-ASCII")),
                          crumb.getBytes(Charset.forName("US-ASCII")));
              }
          }
          return false;
      }
docs: {@inheritDoc}