Create a text file with the following content:
# One.com credentials used by Certbot
dns_onecom_username = johndoe
dns_onecom_password = hunter2
Run the following command: sudo certbot certonly -d \*.example.com -d example.com -a dns-onecom
When prompted for the config file, enter the path to the above text file.
Since One.com doesn't have an official API this plugin is made by reverse engineering the web interface and uses web scraping.
This means it might stop working any time or even worse, do something unexpected. Use at your own risk. I do use this myself though until I change to a better DNS provider though.
This is plugin is more or less made by modifying
certbot-dns-ispconfig
and
certbot-dns-gratisdns.