PHP: Enable sessions ($_SESSION) in WordPress plugins and themes

session-activator.php

<?php
/*
Plugin Name: Session Activator
Description: Enable the use of sessions ($_SESSION) in plugins and themes.
Version: 1.0.0
Author: Christian Tang
Author URI: http://christiantang.dk
*/
add_action('init', 'session_activator_start', 1);
add_action('wp_logout', 'session_activator_end');
add_action('wp_login', 'session_activator_end');

function session_activator_start() {
    if(!session_id()) {
        session_start();
    }
}

function session_activator_end() {
    session_destroy();
}
?>