app.js

// using the http module
var express = require('express')
var app = express()
bodyParser = require('body-parser'),
CryptoJS = require("crypto-js");
const path = require('path');

//Get the signed request parser
var decode = require('./parse-signed-request.js');

//Content
app.use('/views', express.static(path.join(__dirname, 'views')))
app.set('view engine', 'ejs');
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ entended: true }));

// look for PORT environment variable, 
// else look for CLI argument,
// else use hard coded value for port 8080
const port = process.env.PORT || process.argv[2] || 8080;
var consumerSecret = process.env.CANVAS_CONSUMER_SECRET;

//Define request response in root URL (/)
app.get('/', function (req, res) {
  res.json({'context': 'Welcome to the Sample Canvas back-end API. Please refer to the links for further calls.','links': [{'name': 'canvas-demo', 'href': '/canvas-demo/'}] });
  res.end();
})

//Return for the fixed page 
app.get('/canvas-demo/',function(req,res) {
  res.render('index', { context: "", url: process.env.IMAGE_URL});
});

//Signed request for canvas app
app.post('/canvas-demo/', function (req, res) {
  var signed_req = req.body.signed_request;
  var hashedContext = signed_req.split('.')[0];
  var context = signed_req.split('.')[1];
  var hash = CryptoJS.HmacSHA256(context, consumerSecret);
  var b64Hash = CryptoJS.enc.Base64.stringify(hash);
  if (hashedContext === b64Hash) {

    //Decode context
    body = JSON.stringify(req.body); 
    data = JSON.stringify(res.data);
    
    signed_request = JSON.parse(body)['signed_request']

    var json = decode(signed_request, process.env.CANVAS_CONSUMER_SECRET);

    //Render and pass
    res.render('index', { context: json, url: process.env.IMAGE_URL });
 } else {
    res.send("Canvas authentication failed");
  };
})


//Launch listening server on port Heroku-capable port
app.listen(port, function () {
  console.log('App listening as would be expected!')
})

//Export for tests
module.exports = app;