Created Unassigned: CandidateAction internal class [1450]

Is there a specific reason why the CandidateAction (System.Web.Http.Routing) class has been marked internal? I was trying to copy some source code from DefaultHttpControllerSelector (System.Web.Http.Routing) class but was unable to do so because it couldn't find the CandidateAction (since it's internal).

Or is there a better way to implement a custom HttpControllerSelector that also supports attribute routing and other new features?