public function getUserLoginFromUserEmail($userEmail)
    {
        Piwik::checkUserIsNotAnonymous();
        Piwik::checkUserHasSomeAdminAccess();

        $this->checkUserEmailExists($userEmail);

        $user = $this->model->getUserByEmail($userEmail);

        // any user with some admin access is allowed to find any user by email, no need to filter by access here

        return $user['login'];
    }