Attribution service for Android and iOS

Hello, I am interested in building in-house attribution service for our apps. Such as a user is brought to google play/app store via tracking url. It is easy to get parameters from url for android and then once some action (which we wish to track) happens, we will be able to send it back as conversion to our service using referrer api. The problem mainly is with iOS... We need a solution for unity (both ios, android) and for single android and ios apps.