Certbot
Installation
Install certbot in your current environment
# nix-env -iA nixos.certbot
Usage
DNS challenge
The following command will generate a SSL certificate key pair for the domain example.org using the DNS authentication mechanism. After running this command, you'll get asked by the script to paste a specific key into your DNS records for example.org.
# certbot certonly --manual --preferred-challenges dns -d example.org --register-unsafely-without-email --agree-tos
If everthing went well you'll have the certificate and key file stored as /etc/letsencrypt/live/example.org/fullchain.pem and /etc/letsencrypt/live/example.org/privkey.pem