Dear PiBa,
Thank you very much for communicating positively instead of just laughing out loud! It is indeed possible to upload any consistent certificate (regardless of CN and the like) to the cert manager and the acme package will overwrite it, if set up correctly, while retaining the private key. Hence, generating certificates suitable for private key pinning is well possible.
There is one other issue I am trying to resolve: For some applications, I do need certificates outside pfsense, for example for starttls in my e-mail gateway. Instead of generating separate certificates for those servers via lets encrypt, it is conceivable to reuse the certificates generated and renewed by pfsense there. While I do backup the configuration nightly via ssh which seems to contain the certificates and keys in clear text, is there a convenient way to download (or export) individual certificates and keys via a bash script based on the content of config.xml?
Regards,
Michael