So i found the following for Drupal https://forum.nginx.org/read.php?2,220510,220563#msg-220563

http {
map $http_cookie $session_id {
default '';
~SESS(?<session_guid>[[:alnum:]]+) $session_guid;
}
}

server {
location ~ \.php$ {
fastcgi_cache_key $session_cookie$request_method$scheme$host$request_uri;
}
}

And want to implement it for Joomla but Joomla's cookies regex do not contain "SESS", Wanted some help to modify this for a Joomla environment so the pages cached and served when registered users are logged in they will only receive their own pages because of the cookie matching with the key.

Example Joomla based site that session cookie format can be seen. http://www.networkflare.com/