Let's say Site A is a traffic generating website. User A clicks on a banner on Site A and gets redirected to Site B (for example a landing page). From Site B there is a link to Site C (which is for example Facebook, Google, or any other big company).
Question: How can Site C determine which sources did User A come from? Becuase I have seen a lot of Site C websites that knew which was Site A.
As far as I know, browsers cannot pass Site A referrer url to Site C. How do they do it anyway? Are they using any kind of PHP or Javascript code for that?