1) If the intranet offers WiFi, you're good to go, any http request will be routed to the correct local boxes.
2) HTTP requests, treat it like you'd treat an external site.
3) If you don't have WiFi, consider setting up a VPN and then in your app guide the user through setting up the VPN. Or, set up a external server (outside the intranet) that acts as a proxy to the intranet server, requiring some sort of auth before it forwards requests for you. Essentially acting as a gate keeper.