Exactly. You have access to quite a bit of information about the user when they make a request, so modifying the response based on any of that information is r

Exactly. You have access to quite a bit of information about the user when they make a request, so modifying the response based on any of that information is really very easy. IP address, cookies you set, browser type, there's lots of info stored in the request headers, you just have to decide what you want to look for and what you want to change.