I'm trying to mirror a site use form authentication. I used 
the url capture and the mirroring works.

However, there are links to other pages which requires 
authentication too. HTTrack fails to capture those, so I 
did a url capture on those links, and add them to the url 
download list.

From what I see, HTTrack makes a copy of the page with some 
random numbers prepended. However, it doesn't converts the 
links to the copied pages. I end up with multiple copies of 
the site, where each one can only access one authenticated 
page.

I understand this link conversion steps will make the post 
processing much longer, but the mirroring would be 
otherwise less perfect.