Do users need to authenticate to access their preferences page?

I’ve read about pref pages, which would be very interesting for me to use, as users could choose for different interests via this page. Right now i think the interests would be set as different segments, the user can enable/disable.

Is this possible?
Is it possible for a user to opt-in into a segment via the prefpage?
Or is it only meant to opt-out (re-opt-in) once you was put there by a campaign or the admin?
Do users need to register to be able to get to the prefpage?
How is the page secured if it was accessible without login?

If the segment is marked visible in preference page .

It’s generally accessible by unsubscribe link, and it’s a tokenized link. Accessible by anyone with the link.