Auto-login user after registering with User Registration

<?php
// http://www.gravityhelp.com/forums/topic/form-direct-to-private-page-with-auto-login#post-97328
add_action('gform_user_registered', 'gf_autologin', 10, 4);
function gf_autologin($user_id, $config, $entry, $password) {
    wp_set_auth_cookie($user_id, false, '');
}