We set only allowed users can access to few categories of youtube. Anyway the Youtube filter not really effective as it still allowed users to watch all youtube categories.
For Example, the link https://www.youtube.com/watch?v=058s3smFXx0 is under "Film" of Youtube category and this is actually not allowed. But user still able to access it.
Release : 188.8.131.52
From the trace, https://www.youtube.com/watch?v=058s3smFXx0 is referrer url,
And the referrer is in film category,
So, need to use request.header.Referer.url.category to block it -- add following lines in the CPL layer,