Application & Authentication

Hi,

I'm a bit concerned about a 'conceptual' issue.

I'm working on a web based app and am using postgresql
 users/groups for authentication, and using functions
/rules/views to ensure users only access/modify their own data.

i.e. many references to 'current_user'

However, in my travels around sf.net, freshmeat etc I haven't come
across any projects built like mine which is concerning to me.

Other projects I've seen use their app for authentication/security
and bypass/ignore the extremely 'useful' security system built into
postgresql and build their own security/authentication system.

I'm wondering if the reason for this is:

A) Necessity.
i.e. Their project frontends run on a mysql backend - and has
to do 'everything'

OR

B) There is some horrible limitation that is going to ruin my day down
the track

Thanks for any comments,

Sean