Rust - Certificate Checker

During my time as an incident manager one of the issues we'd commonly run into would be SSL certificate expiry. This can render an operation dead in the water (Along with DNS providers, long story for another post).

As operations scale, certificates can fall into the "Forgot about that one" status. This is a killer as eventually a certificate you forget about may just be the one you need.

The Site Reliability Engineering team at one of my previous places used to use Wavefront to monitor certificates and while it worked, it wasn't what I would call smooth operating.

We have a few tools we can use to uncover certificates for public facing services and to monitor these certificates. Firstly, (https://crt.sh) crt.sh will crawl through registered subdomains and give you a nice list of certificates.

Secondly, I've slapped together a quick tool in rust that will read from a plaintext file, a list of urls for the tool to check.

My usage will be to have this run on a cron job with postfix sending out emails if a certificate (Which as you can see, facebook only has 7 days left!) is due to expire. A simple script will be able to complete this check and send it out.

Better than Wavefront? - I don't know.
It's free though and it's clear, concise and did I mention free?

You can also compile it onto any platform you choose.
Me from 2019 would have appreciated this, maybe someone else out there will too.