Cookie information between service

I'm running Joomla as my content management system (I'm running this site hosted by godaddy), in Joomla, I'm using an iframe (wrapper) to include my ftp server (using Rumpus on a local machine), so I wanted to authenticate based on the cookies Rumpus is creating (because I can't alter their code), but is there a way to get the cookies if they are based on another host? I haven't found a way yet to do it, maybe someone with a good idea? Robin