Mailu/webmails/roundcube/mailu.php

<?php

class mailu extends rcube_plugin
{

  function init()
  {
    $this->add_hook('startup', array($this, 'startup'));
    $this->add_hook('authenticate', array($this, 'authenticate'));
    $this->add_hook('login_after', array($this, 'login'));
    $this->add_hook('login_failed', array($this, 'login_failed'));
    $this->add_hook('logout_after', array($this, 'logout'));
  }

  function startup($args)
  {
    if (empty($_SESSION['user_id'])) {
        $args['action'] = 'login';
    }

    return $args;
  }

  function authenticate($args)
  {
    if (!in_array('HTTP_X_REMOTE_USER', $_SERVER) || !in_array('HTTP_X_REMOTE_USER_TOKEN', $_SERVER)) {
        header('HTTP/1.0 403 Forbidden');
        die();
    }
    $args['user'] = $_SERVER['HTTP_X_REMOTE_USER'];
    $args['pass'] = $_SERVER['HTTP_X_REMOTE_USER_TOKEN'];

    $args['cookiecheck'] = false;
    $args['valid'] = true;

    return $args;
  }

  function logout($args) {
    // Redirect to global SSO logout path.
    $this->load_config();

    $sso_logout_url = rcmail::get_instance()->config->get('sso_logout_url');
    header("Location: " . $sso_logout_url, true);
    exit;
  }

  function login($args)
  {
      header('Location: index.php');
      exit();
  }
  function login_failed($args)
  {
      header('Location: sso.php');
      exit();
  }

}