socket.io and express.js to share session

Question

I came across this solution for sharing sessions between socket.io and express.js: Second answer (user xpepermint) in this post: socket.io and express 4 sessions

Unfortunately I am stuck with the bit of code below, as variable io sits in config/socketio.js and variable session sits in config/express.js :

io.use(function(socket, next) {
  session(socket.handshake, {}, next);
});

Where do I put and how do I adapt the bit of code above?

My app.js file looks like the following:

'use strict';

import express from 'express';
import mongoose from 'mongoose';
mongoose.Promise = require('bluebird');
import config from './config/environment';
import http from 'http';

// Connect to MongoDB
mongoose.connect(config.mongo.uri, config.mongo.options);
mongoose.connection.on('error', function(err) {
  console.error('MongoDB connection error: ' + err);
  process.exit(-1);
});

// Populate databases with sample data
if (config.seedDB) { require('./config/seed'); }

// Setup server
var app = express();
var server = http.createServer(app);
var socketio = require('socket.io')(server, {
  serveClient: config.env !== 'production',
  path: '/socket.io-client'
});

global.clients = [];
global.socketio = socketio; //added
require('./config/socketio').default(socketio);
require('./config/express').default(app);
require('./routes').default(app);

// Start server
function startServer() {
  app.angularFullstack = server.listen(config.port, config.ip, function() {
    console.log('Express server listening on %d, in %s mode', config.port, app.get('env'));
  });
}

setImmediate(startServer);

// Expose app
exports = module.exports = app;