I strongly suspect the identification page to be a 
form-based page, that is, a page with a username and 
password textfields embedded.
These pages can not be downloaded using basic 
authentication, but you can capture the login page 
through:
Add URL/Capture URL

This is not very simple to do, as you have to 
temporary change your browser's proxy settings, but 
the capture tool should give you a working URL (see in 
the Documentation, interface)