I also use caddy, for my personal sites and I also have a work site that is a bunch of TLS redirectors for domains that the company owns to redirect to other domains. It works spectacularly in those use cases. At the time I set it up it wasn't possible to do that with an S3 endpoint, but now it is.

I do have an haproxy setup that does the right thing with LetsEncrypt, but it's just a path-based forwarder that works with an acme script on the system, not directly built in.

Hopefully it comes soon: https://github.com/haproxy/haproxy/issues/1864

ACME support must be integrated, this was turned into a mandatory feature nowadays…

Stay tune (tips: dataplaneapi)