Hey!
I think I've figured out what was your problem.
You have created a mapping to allow OS user "foobar" auth as pg role "postgres".
What happens though (and error message actually indicates that) is you are trying to authenticate as pg role "foobar". This is probably due to you executing `psql` in terminal without specifying an actual user name.
The way to do this properly would be to execute `psql -U postgres`.
Unfortunately, you've left before I was able to tell you this.
Kind regards,
Nick.