public function permissions()
    {
        $permissionModel = config('defender.permission_model');
        $permissionRoleTable = config('defender.permission_role_table');
        $roleKey = config('defender.role_key');
        $permissionKey = config('defender.permission_key');

        return $this->belongsToMany($permissionModel, $permissionRoleTable, $roleKey, $permissionKey)->withPivot('value', 'expires');
    }