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:

car_portal=> \h GRANT
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 { [ GROUP ] role_name | PUBLIC } [, ...] [ 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 -h localhost -U postgres -d car_portal
car_portal=# REVOKE ALL ON DATABASE car_portal FROM public;
REVOKE
car_portal=# \q

$ psql -h localhost -U web_app...