Authentication blues

I'm working on a PL/SQL set of functions to handle user access
restrictions to particular tables and am wondering:

- Is it "safe" to use postgresql authentication? Should I (like a LOT
of apps do) build my own authentication tables and just use a common
login/password for the application?

I'm honestly curious. My own suspicion is postgres authentication
(using postgres users/groups) is .. for the most part... safer.

also - are there any examples of per-record restrictions on a username
basis in pl/sql? I've been working on this a couple weeks and am
stuck - and can't find any examples on either postgresql or oracle.
(Oracle has the feature built-in from what I can tell...)

Ta!