How do I read values (PHP defined constants) from wp-config.php?

Question

I need to get username, password etc from the wp-config file to connect to a custom PDO database.

Currently I have another file where I have this info, but

Answer 1

I have even defined my own constants in in wp-config.php and managed to retrieve them in theme without any includes.

wp-config.php

define('DEFAULT_ACCESS', 'employee');

functions.php

echo "DEFAULT_ACCESS :".DEFAULT_ACCESS;

outputs DEFAULT_ACCESS :employee