postgres authentication question

By default my installation via Debian set the user postgres to authenticate as a
local, ident sameuser.

This is convenient for someone with a local account.

I'm putting a postgresql installation into my DMZ and want to make sure I have
an understanding of what makes sense and what does not in terms of security.

I would like to change the postgres user to authenticate by md5 only, no ident
sameuser option.  I might still keep the authentication as local only.  But when
I do this, at start up I get a number of minor errors in my logs about the user
postgres can't authenticate.


How do I fix this securely?
-or-
How do I safely disable this?
-or-
Is this a non-problem and should be ignored?