STS is not required for Windows authentication, with .NET 4.5 Claims are included in framework, in fact no extra setup/configuration is required to support Claims. Moreover STS is required only if you are trying to federate.
See How-To
It is not a good idea to deploy a custom developed STS to production environment, you should be using ADFS or Thinktecture.IdentityServer.v2 or any other similar product for federation.