If you're concerned about leaking your servers IP address which could result in a DDoS, this YouTube video will explain how to install TinyProxy and configure XenForo to hide your servers IP address.
This thread has a lot of useful information:
https://xenforo.com/community/threads/recommended-http-proxy-for-config-http-proxy.169192/
This thread has a lot of useful information:
https://xenforo.com/community/threads/recommended-http-proxy-for-config-http-proxy.169192/