Hah. Funny that this post was bubbled up to the top of my thread list, what with the new Firewall module!
Consider your challenge accepted, run with, and complete, @dicko!
As we discussed on IRC, CSF isn’t open source, (in fact, their licence says you can’t even look at the source!) so we couldn’t use that. But I think everyone’s pretty happy with the (100% real AGPL v3+ FOSS) Firewall module.