nginx 如何只反向代理到网站的二级目录

我 nas 上 bt 的路径是 olddomain.myqnapcloud.com:60080/rutorrent/ 原来的配置是这样的,这样我访问的时候是 newdomain.com/rutorrent/。但我想把结尾的 rutorrent 去掉

就是访问 newdomain.com ，反向代理到 olddomain.myqnapcloud.com:60080/rutorrent/ 求指点，感谢感谢

server
        {
                listen 80;
                server_name newdomain.com;

                if ($http_user_agent ~* (baiduspider|360spider|haosouspider|googlebot|soso|bing|sogou|yahoo|sohu-search|yodao|YoudaoBot|robozilla|msnbot|MJ12bot|NHN|Twiceler)) {
                return  403;
                }

                location / {
                sub_filter olddomain.myqnapcloud.com:60080 newdomain.com;
                sub_filter_once off;
                proxy_set_header X-Real-IP $remote_addr;
                proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
                proxy_set_header Referer http://olddomain.myqnapcloud.com:60080;
                proxy_set_header Host olddomain.myqnapcloud.com:60080;
                proxy_pass http://olddomain.myqnapcloud.com:60080;
                proxy_set_header Accept-Encoding "";
                }
}