PostgreSQL security levels

PostgreSQL has different security levels defined on PostgreSQL objects, including tablespace, database, schema, table, foreign data wrapper, sequence, domain, language, and large object. One can have a peek into different privileges by running the \h meta command in psql, as follows:

Command: GRANT
Description: define access privileges
Syntax:
GRANT { { SELECT | INSERT | UPDATE | DELETE | TRUNCATE | REFERENCES | TRIGGER }
    [, ...] | ALL [ PRIVILEGES ] }
    ON { [ TABLE ] table_name [, ...]
         | ALL TABLES IN SCHEMA schema_name [, ...] }
    TO role_specification [, ...] [ WITH GRANT OPTION ]

Database security level

To disallow users from connecting to the database by default, one needs to revoke the default database permissions from public, as follows:

$ psql car_portal -U postgres
psql (10.0)
Type "help" for help.
car_portal=# REVOKE ALL ON DATABASE car_portal FROM public;
REVOKE
car_portal=# \q
$ psql car_portal -U web_app_user
psql: FATAL: permission denied...