Sign on as different user to SharePoint 2010 site published through TMG 2010

As of Service Pack 1, TMG now officially supports publishing SharePoint 2010 sites. If you have tried this you may have ran into an issue when trying to use the “Sign in as Different User” functionality. Fortunately Microsoft has released an update that resolves the issue.

http://support.microsoft.com/kb/2445386

The update is included in Software Update 1 rollup 3 for TMG SP1. This rollup can be found here:

http://support.microsoft.com/kb/2498770

However, just having applied the rollup does not solve the issue.  You will also need to run one of the following scripts on one of your TMG front ends.

For HTML Forms Authentication with Kerberos Constrained Delegation:

Const SE_VPS_GUID = "{143F5698-103B-12D4-FF34-1F34767DEabc}"
Const SE_VPS_NAME = "EnableSharepointSignIn"
Const SE_VPS_VALUE = true
 
Sub SetValue()
 
    ' Create the root object.
    Dim root  ' The FPCLib.FPC root object
    Set root = CreateObject("FPC.Root")
 
    'Declare the other objects that are needed.
    Dim array       ' An FPCArray object
    Dim VendorSets  ' An FPCVendorParametersSets collection
    Dim VendorSet   ' An FPCVendorParametersSet object
 
    ' Get references to the array object
    ' and to the network rules collection.
    Set array = root.GetContainingArray
    Set VendorSets = array.VendorParametersSets
 
    On Error Resume Next
    Set VendorSet = VendorSets.Item( SE_VPS_GUID )
 
    If Err.Number <> 0 Then
        Err.Clear
 
        ' Add the item.
        Set VendorSet = VendorSets.Add( SE_VPS_GUID )
        CheckError
        WScript.Echo "New VendorSet added... " & VendorSet.Name
 
    Else
        WScript.Echo "Existing VendorSet found... value- " &  VendorSet.Value(SE_VPS_NAME)
    End If
 
    if VendorSet.Value(SE_VPS_NAME) <> SE_VPS_VALUE Then
 
        Err.Clear
        VendorSet.Value(SE_VPS_NAME) = SE_VPS_VALUE
 
        If Err.Number <> 0 Then
            CheckError
        Else
            VendorSets.Save false, true
            CheckError
 
            If Err.Number = 0 Then
                WScript.Echo "Done with " & SE_VPS_NAME & ", saved!"
            End If
        End If
    Else
        WScript.Echo "Done with " & SE_VPS_NAME & ", no change!"
    End If
 
End Sub
 
Sub CheckError()
 
    If Err.Number <> 0 Then
        WScript.Echo "An error occurred: 0x" & Hex(Err.Number) & " " & Err.Description
        Err.Clear
    End If
 
End Sub
 
SetValue

For Integrated Authentication with Kerberos Constrained Delegation: You will need to run the script above as well as the script below.

Const SE_VPS_GUID = "{143F5698-103B-12D4-FF34-1F34767DEabc}"
Const SE_VPS_NAME = "UseOnlyNTLMForWindowsAuth"
Const SE_VPS_VALUE = 1
 
Sub SetValue()
 
    ' Create the root object.
    Dim root  ' The FPCLib.FPC root object
    Set root = CreateObject("FPC.Root")
 
    'Declare the other objects that are needed.
    Dim array       ' An FPCArray object
    Dim VendorSets  ' An FPCVendorParametersSets collection
    Dim VendorSet   ' An FPCVendorParametersSet object
 
    ' Get references to the array object
    ' and to the network rules collection.
    Set array = root.GetContainingArray
    Set VendorSets = array.VendorParametersSets
 
    On Error Resume Next
    Set VendorSet = VendorSets.Item( SE_VPS_GUID )
 
    If Err.Number <> 0 Then
        Err.Clear
 
        ' Add the item.
        Set VendorSet = VendorSets.Add( SE_VPS_GUID )
        CheckError
        WScript.Echo "New VendorSet added... " & VendorSet.Name
 
    Else
        WScript.Echo "Existing VendorSet found... value- " &  VendorSet.Value(SE_VPS_NAME)
    End If
 
    if VendorSet.Value(SE_VPS_NAME) <> SE_VPS_VALUE Then
 
        Err.Clear
        VendorSet.Value(SE_VPS_NAME) = SE_VPS_VALUE
 
        If Err.Number <> 0 Then
            CheckError
        Else
            VendorSets.Save false, true
            CheckError
 
            If Err.Number = 0 Then
                WScript.Echo "Done with " & SE_VPS_NAME & ", saved!"
            End If
        End If
    Else
        WScript.Echo "Done with " & SE_VPS_NAME & ", no change!"
    End If
 
End Sub
 
Sub CheckError()
 
    If Err.Number <> 0 Then
        WScript.Echo "An error occurred: 0x" & Hex(Err.Number) & " " & Err.Description
        Err.Clear
    End If
 
End Sub
 
SetValue

Once this is complete you should be able to Log in as a Different User to your hearts content.

I hope this helps!