bbPress.org

In bb-config.php

define('BB_AUTH_KEY', 'WP's AUTH KEY halmstad');

define('BB_SECURE_KEY', 'WP's SECURE KEY halmstad');

define('BB_LOGGED_IN_KEY', 'WP's LOGGED IN KEY halmstad');

Also make sure you have the salts:

define('BB_AUTH_SALT', 'WP's AUTH SALT');

define('BB_LOGGED_IN_SALT', 'WP's LOGGED IN SALT');

And that you have these defined:

$bb->secure_auth_cookie = 'wordpress_sec_456c71223b3bb9958349ec3d65b850f6';

$bb->logged_in_cookie   =  'wordpress_logged_in_456c71223b3bb9958349ec3d65b850f6';

Personally, I set my cookie domain to .domain.se for both WP and BB.