Hi,
I understand that you are trying to use Authentication text as the mechanims.
But for testing putpose, please make the following changes & check if they work:
Change Type field in external CP profile to Radius Authentication
Make the following changes to the HTTP POST:
<form method=POST action="http://securelogin.arubanetworks.com/cgi-bin/login">
<input type="hidden" name="user" id="user" type="text" value="test" class="text" accesskey="u" />
<input type="hidden" id="password" name="password" type="text" value="test123" class="text" accesskey="p" />
<input type="hidden" name="cmd" value="authenticate" />
<input type="submit" name="Login" value="ACCEPT" class="button" />
Add a username/password viz test/test123 in the internal database of the IAP
When the user clicks on Accept button, the credentials (test/test123) are posted back to IAP & get authenticated against internal database & eventually user is redirected to www.msn.com.
This happens in the background & user is never aware of it.