LetsEncrypt with DNS-01 validation for Unifi
Update 2021-01-08: this is now out of date. See my updated post with a much easier method.
I have a number of Ubiquiti UAPs, and I manage them with the UniFi app, installed on a linode server. Like any publicly hosted server, i want to use a trusted SSL certificate, and for that, I chose LetsEncrypt with DNS-01 validation, as i found a useful helper script by thatsamguy on the UniFi forums. I use AWS Route53 to host the DNS zone.