You might want to take a look at the source code, then, and also check out the older manual installation guides. Almost all configuration options are described in the PDF manual. Most of the information in the PDF manual applies to the current ISPConfig version. Only the initial install guide has been replaced with guides available online.
Only two clients, mainly acme.sh and then certbot, and both of them are only supporting http validation at the moment. And as said, other than the above mentioned, they are readily available in main ispconfig website and this forum. As most of us simply volunteer, we do not intend to spoonfeed anyone as they are all easily "self learnable" (if there are such english words ).