Certbot

Certbot is a useful utility for obtaining certificates from the Let’s Encrypt project. This is a free service and can be used both for web and other services like email and WiFi.

The utility establishes proof-of-ownership a couple different ways. The normal way is by answering a request on port 80. This proves you are at least in control of a server. But you can also use DNS when you don’t want to open a given server up to the internet.

You can also request wildcard certs via the DNS challenge. These are useful both when you’re hosting many sites, but also when you don’t want to advertise to the world the sites you are hosting.