If you use the catchurl tool through WinHTTrack it will generate everything you
need to run via command line.

The catchurl proxy does indeed capture data and save a file. It basically
intercepts login form submission data and saves it to a file: hts-post0,
hts-post1, etc.  You can look inside that file to see what's captured (even
change it if desired).

The reference to "login.php>postfile:hts-post0" is saying that HTTrack will
use the "hts-post0" data to submit the form on login.php