Track users browser activity against specified web application

I want to track users’ real-time interaction against the specific site(web app) page and scrap the data he/she views and extract it.

Note: The application is not owned by us so we can’t use google analytics or other libraries similar to it.

Is this possible to implement? and what is the best way to do this?
Any existing tools which we can use to support this requirement??
Any available browser extension or can we develop such an extension? (Note: We can install the extension on our user’s browser)

A similar question is also raised on StackOverflow Tracking user activity with Chrome extension but no answers against the same