My registrar is using a custom script for updating the _acme-challenge TXT, and none of the available services allows just running a command, eg. curl or ddclient. None that I can find anyway.
Is it possible in some other way?
Thanks!
If you want to keep that registrar, and if you are able to create arbitrary DNS entries, you could use DNS alias delegation to another domain on a FreeDNS provider for _acme-challenge.yourdomain.com.
Your registrar should put up a script and see that it gets included in ACME.sh (https://github.com/acmesh-official/acme.sh/tree/master/dnsapi). When the new version gets included in OpnSense, it can be used natively.
What registrar is that?