server.js

var express = require('express')
var app = express()
const cors = require("cors");

app.use(cors({
  credentials: true,
  origin: process.env.CORS_ORIGIN
}));

if (process.env.NODE_ENV === 'production') {
  app.set('trust proxy', 1) // trust first proxy
}

var session = require('express-session')
app.use(session({
  secret: process.env.EXPRESS_SESSION_SECRET,
  resave: true,
  saveUninitialized: true,
  cookie: {
    sameSite: process.env.NODE_ENV === "production" ? 'none' : 'lax',
    secure: process.env.NODE_ENV === "production",
  }
}))

const mongoose = require('mongoose');
mongoose.connect(process.env.MONGODB, {useNewUrlParser: true, useUnifiedTopology: true});


/// configures CORS
app.use(function (req, res, next) {
  res.header('Access-Control-Allow-Origin', 'https://aliu19.github.io');
  res.header('Access-Control-Allow-Headers',
      'Content-Type, X-Requested-With, Origin');
  res.header('Access-Control-Allow-Methods',
      'GET, POST, PUT, PATCH, DELETE, OPTIONS');
  res.header('Access-Control-Allow-Credentials', 'true');
  next();
});

var bodyParser = require('body-parser')
app.use(bodyParser.urlencoded({ extended: false }))
app.use(bodyParser.json())

require("./controllers/book-list-controller")(app)
require("./controllers/user-controller")(app)
require("./controllers/review-controller")(app)

require('dotenv').config();
app.listen(process.env.PORT || 4000)