Is it possible to authenticate to a proxy from outside a firewall through nat? I need to filter a few laptops and want to have them come in from the internet through our firewall to a border proxy and then go back out through our internet filter. This is just a band-aid until I can get a new filter/proxy server.

Client--> Inernet-->Fortigate Nat --> BMGR Proxy --> Fortigate Filter --> Internet

I have proxy setup and it works fine inside the firewall (we are only using proxy services and no filtering). I setup a NAT to a brdr server but it redirects to an internal only ipaddress. 172.x.x.x and not the nat address. Is there an alternative IP address setting in the proxy.cfg that can switch it? I only need this to work from the outside, so if need be I could put it on the DMZ directly but was trying to avoid that.