Cache: check the whole cache key in addition to hashes. This prevents a potential attack that discloses cached data if an attacker will be able to craft a hash collision between some cache key the attacker is allowed to access and another cache key with protected data. See http://mailman.nginx.org/pipermail/nginx-devel/2015-September/007288.html. Thanks to Gena Makhomed and Sergey Brester.