Session Id is not coming in model laravel

I have a user model in which session user id is not coming below is my code

$authId =  Auth::id();

this is my function in which i want to use session user Id

public static function getPermission(){

        $authId =  Auth::id();

        $result = DB::table('erp_permissions')->select('erp_permissions.id as permission_id','erp_permissions.user_id','erp_permissions.status','erp_sections.id as section_id','erp_modules.id as module_id', 'erp_sub_modules.id as erp_sub_module_id', 'erp_controllers.id as controller_id','erp_sections.name as section_name','erp_modules.name as erp_module_name','erp_controllers.name as controller_name','erp_sub_modules.action as controller_action')
        ->join('erp_sub_modules','erp_sub_modules.id','=','erp_permissions.sub_module_id')
        ->join('erp_modules','erp_modules.id','=','erp_permissions.module_id')
        ->join('erp_controllers','erp_controllers.id','=','erp_permissions.controller_id')
        ->join('erp_sections','erp_sections.id','=','erp_permissions.section_id')
        ->where('erp_permissions.user_id','=', $authId)
        ->get();

        return $result ;
    }

via Chebli Mohamed