I want to install an extension/change a PostgreSQL setting/check system tables and this requires having superuser permissions.
Unfortunately, we don't give you a superuser role on any of our databases for the security and stability of all our customers.
The default user that comes with your Postgres database is a permissive role that is one step below the superuser and allows you to
GRANT certain privileges to other users, but not all privileges to the same extent as a superuser. For example, you can use the default user to grant
DELETE privileges to other users.
The following DevCenter article contains more information to know more about credentials and managing permissions: https://devcenter.heroku.com/articles/heroku-postgresql-credentials#the-default-credential