I've developed a couple of internal sites for my organization that use integrated authentication. Ultimately we want these sites to be accessible externally to users with domain-joined computers. The sites work as expected on domain computers while on the internal network. The problem comes when I take my laptop home and try to access those sites.

IIS only has integrated authentication enabled for the two sites. When I browse to the site using IE8 I get a username/password prompt asking for domain credentials. I can put those in and it will work, but the goal is to use the cached token for integrated authentication.

Next I reasoned that IE wouldn't response to an integrated auth request (is NTLM the right term for this?) unless the site was trusted. I tried adding the site to Trusted Sites but I get the same behavior as the before. I then added the site to Local Intranet sites and that is where things get weird. I get a generic error page from IE, no error code or anything.

Just for funsies I loaded up Firefox (which I had previously set up to use integrated authentication) and I added this new site to network.automatic-ntlm-auth.trusted-uris. Much to my surprise I was able to load the pages up with no problem at all and saw exactly what I was expecting (including verification that the integrated authentication worked).

My mind is a bit boggled at the moment as I'm not really sure where to go from here. I was hoping some of you may be able to provide some insight.