As per tadman’s comment, Homebrew postgres currently creates an account with the same name as the installing user, but no password. E.g. after my initial install (username david
):
$ psql postgres
psql (12.2)
Type "help" for help.
postgres=# \du
List of roles
Role name | Attributes | Member of
-----------+------------------------------------------------------------+-----------
david | Superuser, Create role, Create DB, Replication, Bypass RLS | {}