WAF (Reverse Proxy) without Logon for internal Networks

Hello,

i use a reverse Proxy (Basic Auth) to protect a internal Server - so every logon has to login first. But now i want to splitt it - so thats only auth is required for Internet and external Networks (VPN, Wireless and so on). For Internal Networks i don't want this aditional Logon.

How can i configure it?

Thanks for your help.