I don't understand what they did with openvpn

[Mibox]

client
dev tun
proto tcp
http-proxy 171.***.***.*; 3128
remote 171.***.***.* 1194
resolv-retry infinite
http-proxy-option VERSION 1.1
http-proxy-option CUSTOM-HEADER ""
http-proxy-option CUSTOM-HEADER "GET http://xxxx.xx HTTP/1.1"
http-proxy-option CUSTOM-HEADER Host xxxx.xx
http-proxy-option CUSTOM-HEADER X-Forward-Host xxxx.xx
http-proxy-option CUSTOM-HEADER X-Forwarded-For xxx.xxxx
http-proxy-option CUSTOM-HEADER Referrer xxxx.xx
nobind
persist-key
persist-tun
remote-cert-tls server
auth SHA512
cipher AES-256-CBC
ignore-unknown-option block-outside-dns
block-outside-dns
verb 3
<ca>
Where I live they configure the openvpn file as above and it works miraculously, I don't know how they installed the openvpn server with the http proxy to make it work.