So I had been using myaddr.tools for a long time. Usually I just use it as a DDNS provider, but they can technically publish _acme-challenge subdomain via a HTTP endpoint. This means that we can get a wildcard cert on all subdomains to avoid showing up on certificate transparency reports.
However, after a few rounds of searching, it seems that the only feasible option is to use the deprecated lego module. Therefore, I made a new somewhat generic module that turns the acme challenge request into a very rudimentary templatable HTTP request.
Verified to be working on my production environment
In theory this can also work for similar providers, but I haven't found others yet. The syntax is flexible enough to specify any key-value pairs to be GET/POST/PUT'd in json/form/query-params.
Source: r/caddyserver · by /u/SodaWithoutSparkles