I read this in the ArubaOS 6.2.0.2 release notes, might be what you need?
Captive Portal Enhancements
This release of ArubaOS introduces the following captive portal enhancements in tunnel and split-tunnel
forwarding modes.
When a client using captive portal authentication gets redirected to the captive portal server, the
controller will send information about the AP group and name of the AP to which the client is trying to
connect in the redirect URL. If the AP name is not configured, the redirect URL will contain the AP MAC
address.