Self-signed certificates for local HTTPS made easy

A grid of lockets representing a safe connection in your browser

While working on a recent client project I had to test for secure cookies and to do so needed to test on an HTTPS connection.

Serving HTTPS locally is a function built into most web servers and frameworks, but the tricky part is to get the necessary certificates. You can generate these by hand, but there is a better way.

Instead of getting your hands dirty with openssl and such, meet a little helper called mkcert.

Not only does it streamline the process of creating self-signed certificates that are great for development, but it also does away with the warning about said certificates by automatically installing a locally-trusted root certificate to your machine and integrating it with your browsers, giving you that nice little green lock for confident client presentations.

It's nice because it just works and even more so, it works on macOS, Linux, and even Windows. Follow the instructions in the projects and you're ready.

anchorUse mkcert with ember-cli

Since the project I was working on happens to be built with Ember.js, here is how you use it together with its CLI.

anchorStep 1: Enable SSL in ember-cli

ember serve supports --ssl, --ssl-key and --ssl-cert to set all necessary input through the command line, but I would recommend generating the keys in the place it expects them to reduce clutter.

If you generate the necessary files in ./ssl where ember-cli expects them by default, you only need to add the --ssl flag.

If you want to serve your project with SSL all the time, you can even put "ssl": true inside your .ember-cli configuration file, removing the need for the flag.

Adding the ssl-key and ssl-cert paths there would work as well, but I think the default location is fine, so we will continue with that.

anchorStep 2: Generate all necessary files

We need to generate the .crt and .key files, as well as make sure that their location will be created when cloning the repository whilst ensuring that the actual files are never committed.

# ember-cli looks for key files in ./ssl relative to the project root
mkdir ./ssl
# Make sure this folder shows up in git
touch ./ssl/.gitkeep

# Add the certificates to your .gitignore file
# Do not commit them to your repository
echo -en '# Ignore self-signed certificates created by mkcert\n /ssl/server.crt\n/ssl/server.key\n' >> .gitignore

Now you can run mkcert to create your certificate. Consider making this command a run script by adding it to the scripts section in your package.json, or creating a shell script file from it that can be added to your repository. If you don't want to do either, you should consider documenting it in your at least.

# Add additional hosts separated by spaces after localhost if necessary
mkcert -install -cert-file ./ssl/server.crt -key-file ./ssl/server.key localhost

anchorStep 3: Profit

Your frontend application is served on https://localhost:4200 now, allowing all the things you would expect from a properly SSL encrypted server connection and in turn, allowing you to replicate and debug real-world situations with ease.

anchorUse mkcert with fastify

When I need to create a quick API and don’t want to use Rust with Actix, I often find myself reaching for fastify. It's a lot like the Express.js used by ember-cli internally, but has a few nice extras and I happened to have used it recently.

If you want to serve HTTP/2 over HTTPS for your fastify API, you will also need certificates.

The documentation for this is quite straightforward. The example there expects fastify.key and fastify.cert in a https folder.

Consider the following structure in your project:

|- src
   |- main.js
|- https
   | .gitkeep
// src/main.js
const fs = require("fs");
const path = require("path");
const fastify = require("fastify")({
  http2: true,
  https: {
    allowHTTP1: true, // fallback support for HTTP1
    key: fs.readFileSync(path.join(__dirname, "..", "https", "fastify.key")),
    cert: fs.readFileSync(path.join(__dirname, "..", "https", "fastify.cert")),

// this route can be accessed through both protocols
fastify.get("/", function (request, reply) {
  reply.code(200).send({ hello: "world" });

fastify.listen({ port: 3000 });

Generate the mentioned files like this:

mkcert -install -cert-file ./https/fastify.cert -key-file ./https/fastify.key localhost

You can now run node ./src/main.js and visit https://localhost:3000 with SSL encryption and your local browser will show a green checkmark as well!


First, you must never share the rootCA-key.pem file created by mkcert with anyone. It must not leave your computer as it would give an attacker power to intercept any secure request to your machine. Handle with care.

Second, the root certificate is what makes your browsers accept the self-signed certificates created by mkcert as valid. That means, only you alone get the benefit of the green lock in your browser. Sharing your development server with someone else on your network or even trying to use them in a public scenario would lead to browsers warning visitors about invalid certificates.

Do not use this in production. It's a neat thing that helps you get your job as a developer done, but once you move to production, you should look for other options.

One of those options would of course be Let's Encrypt.

Yes, you could also use that locally, but from my experience, if you are looking for a quick way to run a local development server with SSL, mkcert really works like a charm.

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