People often ask when should you use the TMG firewall for web publishing versus the UAG server? There are a lot of reasons for choosing either one – but you definitely wnat to use the UAG server when you have advanced authentication requirements, since the UAG server is a lot more robust when it comes to authentication protocols and providers. This article will give you the information you need to know
http://www.isaserver.org/articles-tutorials/configuration-general/forefront-uag-authentication-options.html
HTH,
Deb