How would I automatically insert username/password into .htaccess with livecode?

[Admin]

I want to write my own shopping cart because I need very specific
functionality. 

To do this, I need to open a .htaccess file on the
server, insert a username and password and then save that file. 

Then
the cart will allow them to download multiple files (some are BIG).


How would I go about this? 

Mike