yc-dyndns requires no special privileges and writes no files
and may thus be run as unprivileged user, e.g. via crontab(5):

	# useradd -g =uid -s /sbin/nologin -d /nonexistent _dyndns

certbot with the following /etc/letsencrypt/cli.ini
snippet can be used to facilitate ACME DNS-01 challenge responses:

	authenticator = manual
	preferred-challenges = dns-01
	manual-auth-hook = /usr/local/libexec/yc-dyndns/certbot-hooks/auth -k .../authorized_key.json
