private function normalizeRoleList (array $roles)
    {
        $normalized = [];

        foreach ($roles as $role)
        {
            $roleKey = (is_object($role) && ($role instanceof BaseRole))
                ? $role->getRole()
                : (string) $role;

            if (isset($this->roleCollection[$roleKey]))
            {
                $normalized[] = $this->roleCollection[$roleKey];
            }
        }

        return $normalized;
    }