Handling users

Hi all,

I am writing a small piece of software based on postgresql for an issue
tracking system. I am using DB connection pooling in C++/libpq.

I have couple of questions.

1) I plan to deligate handling user management to postgresql. i.e. I will be
creating database users instead of maintening my own user/password stuff. I
have 500 users right now and the number will grow. Will that cause any
problem fro indexing/performance etc. POV? (I know this is kinda stupid but
just confirming)

2) The connection pool will be initiated as database superuser so that it can
do set session authorisation and revert back on the fly.

In this scheme, how can I authenticate user without fiddling with postgresql
system catalogs? I mean I have and established connection as database
superuser, a username and a password. Now I want to authenticate. How do I do
it?

TIA..

 Shridhar