Let's Encrypt also allows you to do DNS based validation (DNS-01) where you just set a TXT record on the domain and update it from time to time. The acme.sh sc

Let's Encrypt also allows you to do DNS based validation (DNS-01) where you just set a TXT record on the domain and update it from time to time. The acme.sh script actually supports quite a few providers so you can cron it up and never even have to run an out-facing HTTP server. Useful for if say your ISP blocks port 80 or if you're behind a NAT you cannot control.