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Self-Signed SSL (TLS) Certificates on a Local IP Address

RT Cunningham | October 28, 2020 (UTC) | Web Development

TLS local addressFirst things first. SSL (Secure Sockets Layer) is the predecessor to TLS (Transport Layer Security). Since people keep referring to TLS for websites as SSL, that’s what I’ll call it as well. Perhaps someday, no one will use the SSL terminology anymore.

Creating self-signed SSL certificates is relatively easy. Getting them to work with different web browsers can be a challenge. It’s not safe to use them outside a local IP address range, but perfectly safe to use them for local web development.

Localhost and Local Area Network (LAN) IP Address Ranges

The local loopback interface is in the range, with translating as “localhost”. There are differences in how that IP address is treated by certain services, so it’s almost always better to use “localhost”. It’s even better to use “subdomain.localhost” (any name for the subdomain) when working with SSH because cookies are treated differently without a subdomain.

You don’t have to use the localhost, of course. It’s perfectly fine to use one of the IP addresses on your LAN. My laptop computer uses the static IP address of The domain name I use for web development is simple - domain.local. Since I like working with wildcards, my “hosts” file entry is: domain.local first.domain.local second.domain.local

Every project I work on uses a subdomain, making it easy to drop one without affecting the others.

A Self-Signed SSL Wildcard Certificate

This is the command I use for creating a self-signed wildcard certificate, which I just tested today:

openssl req -new -x509 -out domain.local.crt -keyout domain.local.key \
-newkey rsa:2048 -nodes -sha256 \
-subj "/CN=*.domain.local" -extensions SAN -reqexts SAN \
-config <(cat /etc/ssl/openssl.cnf <(printf '[SAN]nsubjectAltName=DNS:*.domain.local')) \
-days 3650

I use 3650 days (about 10 years) because why not?

Web Browsers and Self-Signed SSL Certificates

All web browsers treat self-signed certificates as unsafe, regardless of where you use them. To get rid of the interruptions with Chromium-based browsers, put “chrome://flags/#allow-insecure-localhost” in the address bar and enable it (Brave will change “chrome” to “brave”). With Firefox, when you approve it, it gets added to the exceptions.

There’s a better way. Don’t use SSL at all when doing local web development. If you’re using someone else’s code or CMS, you may not have a choice. When you do it yourself, you always have a choice.

If you want your code to be transportable, make it conditional. With PHP, this is what I do:

$site_url = 'http' . ($_SERVER['SERVER_PORT'] == 443 ? 's' : '') . '://' . $_SERVER['HTTP_HOST'];

HTTP_HOST includes alternate port numbers, when you use them. You can do something similar with cookies, to include the secure flag or not.

Image Attribution: Fabio Lanari, CC BY-SA 4.0, via Wikimedia Commons
Edited and updated. Originally published at one of my other websites in May 2018.

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