static noCacheJson (req, res, next) {
    res.header('Cache-Control', 'no-cache, private, no-store, must-revalidate, max-stale=0, post-check=0, pre-check=0');
    res.header('Content-Type', 'application/json');
    res.header('X-Content-Type-Options', 'nosniff');
    return next();
  }
Express middleware to set some common headers for json responses