BuddyPress.org

https://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/walled-garden-for-buddypress/

And here’s a link to the original thread which is worth reading through.
https://buddypress.org/community/groups/creating-extending/forum/topic/securing-components-from-non-logged-in-users/

I haven’t tested this with the latest version of WP/BP but I’ve used a similar method up to WP 2.9.1 and BP 1.2 without issue.