OpenBSD's 'acme-client' may be a good fit in these kinds of cases - not sure if anyone has ported to other systems but it's probably a pretty direct recompile with maybe a couple of adjustments
The OpenBSD acme-client is OpenBSD specific and lacks a whole bunch of features, it is I suppose exactly what you'd expect the default acme-client to be in OpenBSD and so it fits its role perfectly but it doesn't make any sense as the "standard" ACME client with no support for lots of desirable ACME features.
https://man.openbsd.org/acme-client.conf.5 http://cvsweb.openbsd.org/src/usr.sbin/acme-client/