I'm trying to set up CADDY as a docker container, offering secure reverse proxy to a number of containers/hosts in my home lab. As I'm using a wild card *.johnsnexus.click I'm using a DNS challenge. Do I need to write a TXT file somewhere on your server? And your documentation says "own_domain should be set to the root domain returned from /dns/getroot/{hostname} of the Dynu API." How do I find out the "root domain"? The Caddy container at the moment is stalling as it is not getting a response from the DNS challenge - I think. There are no errors just "INF ts=1743541550.8186793 msg=client retrying in 8.373566775s because of Get "https://api.dynu.com/v2/dns/getroot": EOF". I'm new at this as you can tell. Many thanks.

Caddy does not use wildcard. If you found a way, let me know !
You include all your domains and subdomains in the vhosts of the Caddyfile config, and each one get a unique certificate, not a SNI. I know this is very strange for those like us who worked with Apache and Nginx forever, but once you get it, it's fabulous :-)