It's like Picasa album functionality (
https://picasaweb.google.com/aik.bold/Blogger?authkey=Gv1sRgCP7qwrLcyYmq2gE#), where you can give access to private album with a direct link.
From technical viewpoint it will be pretty easy to implement:
- create 2 fields in a Category table: DirectLinkEnabled (Yes/No) and DirectLinkAuthKey
- when someone enables direct link functionality (on category/section editing page), then
- random alpha-numeric string will be generated and stored in category/section record
- link to that page with freshly generated authentication key will be displayed
- in checkItemStatus method (where check is made to prevent viewing Pending/Disabled categories/sections) also check is authentication key is present in url and it matches one from current category/section record
- if all matches, then show category/section and don't redirect to "no permission" page as usual in this case
If there will be a need, then such approach could be applied to any category item or any page on the site.