.net routing: Possible to restrict route to a certain domain? - asp.net

Question

I inherited a vb.net WebForms project that handles a couple domains. However, I want unique routes for each domain. Is there a way to do this by getting the domain when I use MapPageRoute? Or will I need to do something like:
routes.MapPageRoute("r1", "example1/page1", "~/example1/default.aspx")
routes.MapPageRoute("r2", "example2/page1", "~/example2/default.aspx")
But then the urls will need to be like:
//example1.com/example1/page1 and //example2.com/example2/page1
At Application_Start, I'd like to constrain a route to a specific domain, if possible.
* EDIT *
Ok, it looks like I was able to semi-resolve this by creating unique route names for similar route paths:
routes.MapPageRoute("r1", "page1", "~/example1/default.aspx")
routes.MapPageRoute("r2", "page1", "~/example2/default.aspx")
Then in my markup I can do:
<asp:HyperLink NavigateUrl="<%$RouteUrl:routename=r1%>" ID="link_home" runat="server">Home</asp:HyperLink>
Then in my Default page (or its master page), I can then handle the "//example.com/" request by redirecting to the respective route based on the domain.
However I'm not sure how to handle incoming requests like:
//example1.com/page1 and //example2.com/page1. I assume the first route will load for either domain. Any ideas what I can do?

Answer 1

Follow up to my comment:
You can instead create a constraint based on the domain. You'll need to subclass the IRouteConstraint interface.
Where you define your routes:
Dim domain1Constraint As New HostConstraint("domain1.com")
routes.MapPageRoute("r1", "page1", "~/example1/default.aspx", False, Nothing, New RouteValueDictionary(New With {domain1Constraint }))
Then create a class HostConstraint:
Imports System
Imports System.Web.Routing
Public Class HostConstraint
Implements IRouteConstraint
Private _host As String
Public Sub New(ByVal host As String)
_host = host.ToLower()
End Sub
Public Function Match(ByVal httpContext As HttpContextBase, _
ByVal route As Route, _
ByVal parameterName As String, _
ByVal values As RouteValueDictionary, _
ByVal routeDirection As RouteDirection) As Boolean Implements IRouteConstraint.Match
Dim host As String = httpContext.Request.Url.Host.ToLower()
If host.Contains(_host) Then
Return True
Else
Return False
End If
End Function
End Class