I was able to fix it by adding the following in settings.php:

# Mixed session handling from https:// with http://
$conf['https'] = TRUE;

Right now I have every foo.com request redirecting to www.foo.com and I haven't filled out the secure/insecure url fields. I'm currently running this 'redirect' using Domain Access, do you think using .htaccess would make any performance/SEO difference?

Thanks for you quick reply!