How to use the keystone.app function in keystone

onMount: () => {
    console.info('----\n==> ✅  %s is running with Keystone.', config.app.title);
    console.info('==> 💻  Open http://localhost:%s in a browser to view the app.', config.port);

    const app = Keystone.app;

    app.use(compression());
    app.use(favicon(path.join(__dirname, '../../', 'static', 'favicon.ico')));

    app.use(require('serve-static')(path.join(__dirname, '../../', 'static')));

    app.use(cookieParser(process.env.COOKIE_SECRET));

    app.use((req, res) => {
      if (__DEVELOPMENT__) {
        // Do not cache webpack stats: the script file would change since
        // hot module replacement is enabled in the development env
        webpackIsomorphicTools.refresh();
        res.header('Access-Control-Allow-Origin', '*');
      }
      const client = new ApiClient(req);

keystone.openDatabaseConnection(function () {
	var server = keystone.app.listen(process.env.PORT || 3002, function () {
		console.log('-------------------------------');
		console.log('Keystone server ready on port %d', server.address().port);
		console.log('-------------------------------');
	});
});

onMount: function(){
		var app = keystone.app;
		var express = require('express');
		var renderer = require('react-engine');
		var engine = renderer.server.create({
			reactRoutes: path.join(__dirname,'/public/routes.jsx')
		});

		app.engine('.jsx', engine);
		app.set('views',path.join(__dirname, '/public/views'));
		app.set('view engine','jsx');
		app.set('view', renderer.expressView);
		app.use(express.static('public'));

		app.get('*', function(req,res){
			res.render(req.url);
		});

_helpers.adminEditableUrl = function(user, options) {
		var rtn = keystone.app.locals.editable(user, {
			'list': 'Post',
			'id': options
		});
		return rtn;
	};

export default (app) => {

	keystone.app = app;

	return keystone;
};

_helpers.adminEditableUrl = function (user, options) {
		var rtn = keystone.app.locals.editable(user, {
			list: 'Post',
			id: options,
		});
		return rtn;
	};