The config file: $HOMEBREW_PREFIX/etc/pgbouncer.ini is in the "ini" format and you
will need to edit it for your particular setup. See:
https://pgbouncer.github.io/config.html
The auth_file option should point to the $HOMEBREW_PREFIX/etc/userlist.txt file which
can be populated by the $HOMEBREW_CELLAR/pgbouncer/1.25.2/bin/mkauth.py script.