Browser Access to iCloud Keychain Data

I'm trying to build functionality into a custom browser, for personal use ATM, to emulate how Safari handles autofill for logging onto different sites. I'm unsure where to start. Any ideas/suggestions?

I poked around and can't find a good place to start. Any examples of creating the connection to the iCloud Keychain and retrieving a credential set, would be beyond incredible, but just a pointer or to of where to start looking would help a lot as well.

Thank you!