Serve HTTPS requests with Express and NodeJS

One of the things I do, on my job, is to maintain a javascript library to display ads. Customers will inject this script on their page and voilà they start displaying ads.

Everything works nice and easy except debugging. One of the problems is that we build this big chunk of javascript with customer’s data, a bunch of other open source libraries, all concatenated in one file (there is a reason why we do that - we are not crazy).

So, when we have to debug the library, we usually generate a modified version (uncompressed, or with sourcemaps, or with a different configuration…) and then we inject it into the page. To do that, we use several thecniques:

  • via Requestly (a firefox and chrome plugin) it is possible to redirect a request to localhost
  • by specifying an entry in /etc/hosts we can also redirect traffic for a domain to aother ip, like localhost

The problem is when our target website is on https. As you know, when the page is served on a secure channel, all other requests must be https too. This means that if I require https://michelenasti.com I cannot add a script tag pointing to http://cdn.google.com/jquery.js - the browser will refuse to serve the file and will display a warning in console.

The opposite is not true: if the page is on http, you can link to https files.

So I needed to serve my files over https. How to do that?

Yes, you need to "generate" a certificate.

Generate the certificates

First of all, we need to generate a certificate that will be used by our https server. In the same folder of express index.js, run this command on mac or linux:

$ sudo openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout ./selfsigned.key -out selfsigned.crt

The program will ask you to answer some questions on the issuer of the certificate.

This will generate two files, selfsigned.key and selfsigned.crt, that can be used by any webserver in the world, but for now we’ll use in nodejs.

This step is only required once. Generate and forget :)

Use the certificates in express

in the same folder of the generated certificates, create a file index.js:

const express = require('express');
const fs = require('fs');
const http = require('http');
const https = require('https');

// read the certificate files previously created and create 
// options object for https server 
var key = fs.readFileSync(__dirname + '/selfsigned.key');
var cert = fs.readFileSync(__dirname + '/selfsigned.crt');
var options = {
  key: key,
  cert: cert
};

const app = express();

// this handler will respond to all GET requests. 
// It will respond with the file that matches the url. 
// For example http://localhost:3000/index.js 
// will respond with this very file. 
const handler = (req, res) => {
    res.sendFile(`${req.url}`, {
        root: '.'
    });
}
app.get('*', handler);

// set the server to respond on http and https 
var httpServer = http.createServer(app);
var httpsServer = https.createServer(options, app);

// set the addresses. This will start the program! 
httpServer.listen(3000);
httpsServer.listen(8443);

The first time you run this program, browsers will ask you if you trust this certificate. Then, the server will work flawlessly.

To conclude, I want to point out how easy it is to create an http(s) server with few lines of code and nodejs.

And also, that this server should not end in production. what if a hacker will request `https://your_server:8443/selfsigned.key ? Or some other random file on your hard disk? enjoy :)

Related Posts: