Most likely the site is sending some sort of cookie to establish a session after you've logged in. Since you don't appear to be sending a cookie back they're presuming it's a brand new session. You need to look at using something like WWW::Mechanize to automate logging in and then navigating to download whatever file you're after.

Have you tried including the userid and password in the command line?

 -u/--user <user:password>
              Specify user and password  to  use  for  server  authent
+ication.
              Overrides -n/--netrc and --netrc-optional.
[download]

And have you tried embedding the userid and password in the url?

http:userid:password@url.com
[download]