Need help finding a way to create my bot protection integration app

[fractal1]

I am working on creating an app that would allow shopify stores to take advantage of a 3rd party anti bot service. I am looking for a way to have it serve as a sort of gatekeeper to checking out, however I can't find anything in the docs that would allow this functionality. I was thinking of maybe using the payment customization Function API, but I'm not 100% this will even be able to do what I want securely, and it is only in the developer preview. If anyone has any ideas, please let me know!