Quick shoutout to acme-dns:
Limited DNS server with RESTful HTTP API to handle ACME DNS challenges easily and securely. - acme-dns/acme-dns
https://github.com/acme-dns/acme-dns
It's a project to let you host your own ACME challenge server, for generating your own SSL wildcard certificates. Pretty neat!
Careful if you try to do that, though: exposing port 53 (necessary for DNS resolution, as part of the acme-challenge) will probably flag your machine as abusable for DDoS attacks and get you a notice from the closest national cybersecurity office to your VPS provider, and you by extension.