This works on DSM 6.1 with a custom TLD for NAS (split-horizon DNS), e.g. nas.example.com.
ssh [email protected]
sudo -i
git clone https://github.com/Neilpang/acme.sh
cd acme.sh
./acme.sh --install --nocron --home /usr/local/acme.sh --accountemail [email protected]
cd /usr/local/acme.sh
export CF_Key="examplekey"