Add more options to the express app when using KeystoneJS

keystone.js

var keystone = require('keystone');
var express = require('express');
var body = require('body-parser');
var helmet = require('helmet');  

var app = express();

app.use(body.urlencoded({ extended: false }));
app.use(body.json());
app.use(helmet());

keystone.app = app;
keystone.init({...});