Embedded App and User Authentication

I have an embedded application on MacOS X that bundles the postgresql apps
and a database cluster with the OSX application, but am running into
troubles when trying to launch the application under different usernames.

In particular, if I create a database with 'initdb' under a username user1,
I can launch postmaster pointing to that database cluster on any system I'm
logged into with the username user1. However, as soon as I move to a system
where I'm logged in as user2, postmaster will fail to launch with the error
message "FATAL: role "user2" does not exist" .

Does anybody know of a way around this?

I can't seem to find a way to turn this type of authentication off. I also
looked into creating a 'ROLE' that would give anybody access, but can't see
how to do that.

Thanks for your help,
Jeffrey