How to find out the source of the transition to the VKontakte application?

Question

PHP

Hello! There is an iframe VKontakte application and there is a task: to find out from which of several of my sources the transition to this application was made.
How to solve it? View user's refer? Or is it possible to pass a special parameter to the URL? Or are there other solutions?
Thanks for the answer.

Answer 1

Make the transition parameter in the url for each of the sources. When receiving, check the parameter and find out. This is done almost everywhere for external links.