Here is the modification
https://vborg.vbsupport.ru/showthread.php?t=126007 However, I cannot tell whether or not it has a built in option to turn off/on for specific usergroups without installing it. Adding that option would be simple with a basic conditional though, If you need help with that feel free to ask. Bascially, it won't truly secure the feed, it will just make it so it's not viewable by specific groups.