Single Login across Multiple WordPress Installations

Howdy!

Previous threads have helped me share users between two WordPress installs, but I ran into a problem: When a user logs into one, they’re not logged into the other (and vice versa.) I’d really like to transfer the session between the two and only require users to log in once.

Here’s what I did to share users, if it’s helpful. “Secondary” refers to the WordPress Installation residing within a subdirectory of the “Primary” WordPress Installation:

Added

define(‘CUSTOM_USER_TABLE’, ‘wp_users’);
define(‘CUSTOM_USER_META_TABLE’, ‘wp_usermeta’);

to wp-config.php in Secondary WordPress root.
——————————
Changed

$this->cap_key = $wpdb->prefix . ‘capabilities’;

to

$this->cap_key = ‘wp_capabilities’;

in capabilities.php in wp-includes of Secondary WordPress install

Thank you for all your help!