Request for help

Hi,

We have recently converted our db2 database to PostgreSQL and we stuck on one thing I,e Authentication of users.

Let me explain what was in DB2,

We have a unix group "mhubrpt" on DB2 unix server and have connect permissions to DB2 database for that group.
Whenever user needs access to DB2 database we will add that user to DB2 unix server and assign to group mhubrpt, then
userwas getting access to DB2 database. 
If user wants to connect DB2 database through graphical tool like Toad from any other windows operated machine he used
togive unix server login credential (userid and password) at Tool. 

We are planning to maintain same type of authentication in PostgreSQL, can you please help us.

Thanks,
Veera

Sent from my iPhone