[Dovecot] How do I use a username/password plain text file as authentication backend?

[Angus]

I only have a single user (with multiple mail addresses) and I don't
want to expose local users (no pam or /etc/passwd). Using a SQL
database seems like overkill to me. So why not just a plain text file?
Well, I've read http://wiki2.dovecot.org/PasswordDatabase/Static and
related wiki pages, but I just can't find a clear answer. I certainly
don't want to allow "any user" or "any password". Dovecot 2.0.9. Any
hints for me?