I own a Synology NAS and it now supports the free certificates from Let's Encrypt. The only problem with Synology's implimentation is that they only allow the web (HTTP-01) method of certificate verification. This means that I have to map port 80 and 443 from my NAS and make it available to the Internet. Yuch! This is what I did to use Let's Encrypt and not open up and web ports to the internet.