Question new form validation rule

Hi, 

I first posted this question on Github but it was closed and I was directed to the forum so here I am. (Link)
I am also not sure if this is the correct place to post it, I wanted to make a thread in CodeIgniter 4 DeDevelopment first but wasn't able to make a thread there.

So here is the feature I am thinking about that I would like to make in CodeIgniter:
I want to make a "Have I Been Pwned" form validation rule. As you may know this could contain a lot of logic (more than the average current validation rule), so I was wondering does it all have to be in 1 function or is it okay to split it up in multiple functions in the validation file? Or should I maybe make a seperate file for it? (Kinda like the CC validation)

I really think having this new rule available in CodeIgniter is a good step forward to a modern framework in today's state of the internet.
Any feedback is welcome!