The Team System UE blog has a draft help topic (Walkthrough: Setting up Team Foundation Server with Secure Sockets Layer (SSL) and an ISAPI Filter) that provides a walkthrough for configuring Team Foundation Server for external connectivity using SSL and the AuthenticationFilter ISAPI filter, which shipped in SP1 Beta.
The following walkthrough describes one procedure for requesting, issuing, and assigning certificates that are used for Secure Sockets Layer (SSL) connections in Team Foundation Service Pack 1 (SP1) Beta, configuring Basic and/or Digest authentication, and configuring an ISAPI filter. In order to support external connections to your Team Foundation Server deployments, you must configure Internet Information Services (IIS) to enable Basic and/or Digest authentication. Additionally, you must configure an Internet Server Application Programming Interface (ISAPI) filter.
For more information, see Accessing Team Foundation Server Remotely via the Internet.