How to connect multiple databases's users/roles

Hi. I'm trying to authenticate users against database's user/roles
(PostgreSql), instead use an almighty user set in database.yml
Can i use ActiveRecord::Base.establish_conection() method? And is this
related whit ActiveRecord::Base.allow_concurrency = true and
I know about issues related with this point (Katana Suicide
Concurrency), but I really need connect each system's user as single
database user/role. I think this must be able to do. Thanks.