A Blackberry Playbook has been added to my network, and it's been conigured to use the ISA 2004 FW as an http proxy. Unfortunately, it's access appears to be somewhat "Flakey"
Although you can specify an http proxy server, and the username/password for each Wi-Fi network the device connets to, it always prompts for the username and password when first opening a page with the browser app. After the details have been provided, however, the browser seems to function quite normally. This is slightly irritating, but not a major issue.
The big problem is that pretty much every other application, sends an HTTP packet, gets a 407: Authorization required response from the proxy and prompts the user for their proxy details. Unfortunately, it's then either trying to connect anonymously to the same URL (and getting a 407 again), or sending an anonymous request for the next URL (and re-prompting for credentials).
I'm under a lot of pressure to "just open up the firewall", which I'm obviously reluctant to do.