veloek

Have you checked that the variable “auto_login” is set to true? It should be somewhere near to the top of the file.

themad: To activate the function, you must uncomment some lines in the constructor around line 375:

if ($this->auto_login) {
  add_action('init', array($this, 'auto_login'));
}

I found it just as easy to use the auto_login function already in the plugin.
I just uncommented the line in the constructor and manipulated it a bit to make it work with REMOTE_USER:

public function auto_login() {
    if (!is_user_logged_in() && isset($_SERVER['REMOTE_USER'])) {
        $user_login = end(explode('\\', $_SERVER['REMOTE_USER']));
        $user = get_user_by('login', $user_login);
        if ($user !== FALSE) {
            $user_id = $user->ID;
            wp_set_current_user($user_id, $user_login);
            wp_set_auth_cookie($user_id);
            do_action('wp_login', $user_login);
        }
    }
}

EDIT: This method doesn’t auto create users with SSO.