Authorization problem

Greetings!

I have 2 PostgreSQL users created. I'd like access to a database restricted
only to one of these users. As it is, in pg_hba.conf, any PostgreSQL user
can connect locally to any database whatsoever:

# TYPE DATABASE IP_ADDRESS MASK AUTHTYPE MAP
local all trust
host all 127.0.0.1 255.255.255.255 trust

I have TCP/IP based connections disabled. What I would like would be
something like:

# TYPE DATABASE IP_ADDRESS MASK AUTHTYPE MAP
local test_db ident test_db_map

The problem is that the ident AUTHTYPE can only be used for TCP/IP
connections. How do I tell PostgreSQL that I only want to allow
postgres_user_1 to connect to test_db, and not every user? And how do I do
this without using passwords and TCP/IP connections?

Thanks in advance.

--
______________________________________________________________________
Pedro Fonseca (pedro(dot)fonseca(at)iscte(dot)pt)
Mob.: (+351)964598357
http://www.pedrofonseca.com
ADETTI/ISCTE (Instituto Superior de Cincias do Trabalho e da Empresa)