[vPostMaster] database access

[Bluedog]

I am trying to set up RoundCube webmail which requires access to a
database.

All works well until:

darken:~# su - postgres
postgres at darken:~$ cd /usr/share/roundcube/SQL
postgres at darken:~$ createuser -A -D -P roundcube
Enter password for new user:   mypassword
Enter it again:
CREATE USER
postgres at darken:~$
postgres at darken:~$ createdb -O roundcube roundcubemail
CREATE DATABASE
postgres at darken:~$s
postgres at darken:~$ psql -U roundcube --password -d roundcubemail
Password:

when I get:
psql: FATAL:  IDENT authentication failed for user "roundcube"

So, the question is, how do I add a user to the database so that is can
be accessed?

TIA,

Steve