Why do I need this?
You probably don't. However, if you're a modder who uses their own site and has an update check, or other kind of access to your web site, you may have come across a problem - you can't access Let's Encrypt resources on the version of Java that Mojang ship with their launcher.
What does this do?
It installs the Let's Encrypt certificate at runtime when the mod is loaded.
As a modder, how do I use this?
Just depend on it on CurseForge, and probably your mod. I run the installation of the certificate in the constructor - so no need to even depend on the mod!
But what if I don't want more dependencies?
The code is open source, and is linked at the top. Feel free to wholesale copy and paste bits, abiding by the MIT license :)
What if someone runs it with a Java version which does support Let's Encrypt certificates - aren't you just duplicating work?
Nope - it will only run if it detects a version of Java which doesn't support Let's Encrypt certificates!
Are you affiliated with Let's Encrypt?
Nope. Not at all. They do cool stuff though - if you run a website, you may want to check them out at https://letsencrypt.org/