Since I see people asking for this every now and then I thought I'd code it and share it.
L2Proxy is a simple MITM proxy for your L2 server.
It comes in two parts
The Java side
The L2Proxy service
The Java side can be used on any pack and with any proxy configuration without needing the app. If however you don't wanna mess with proxy configuration you can also use the L2Proxy service which runs a MITM proxy for your players. It is fully cross