How can I determine if an AD group contains a given DirectoryEntry from another (trusted) domain?

Question

I am trying to beef up my code that determines whether a user is a member of a given AD group. It essentially works except when the member of the group happens to be from another (trusted) domain because it is stored as a foreignsecurityprincipal.

Given that I have a valid DirectoryEntry object for both the Group I want to test, and the Account I want to check for, I need a DirectorySearcher Filter string that will allow me to confirm that the account is in that group, even if the account is a foreignsecurityprincipal.

(VB.NET code Sample demonstrating the issue)

Dim ContainerGroup as DirectoryEntry = ... Code to get Group
Dim UserToCheckFor as DirectoryEntry = ... Code to get User

DSearcher = New DirectorySearcher(ContainerGroup, "(WHATCANIPUTINHERE)", New String() {"member;Range=0-5000"}, SearchScope.Base)
DSearcher.AttributeScopeQuery = "member"

'If an object is found, the account was in the group
Return (DSearcher.FindOne() IsNot Nothing)

Answer 1

Okay. Found it. Here's the trick.

I am trying to beef up my code that determines whether a user is a member of a given AD group. It essentially works except when the member of the group happens to be from another (trusted) domain because it is stored as a foreignsecurityprincipal.

(VB.NET code Sample)

Dim ContainerGroup as DirectoryEntry = ... Code to get Group
Dim UserToCheckFor as DirectoryEntry = ... Code to get User

DSearcher = New DirectorySearcher
Dim DSearcher As New DirectorySearcher(ContainerGroup, getLDAPQueryStringUsingSID(containedGroup), New String() {"member;Range=0-5000"}, SearchScope.Base)

Return (DSearcher.FindOne() IsNot Nothing) 


** Helper Methods **

Private Function getLDAPQueryStringUsingSID(ByVal DEObject As DirectoryEntry) As String            
  Return "(objectSid=" + getSDDLSidForDirectoryEntry(DEObject) + ")"
End Function

Private Function getSDDLSidForDirectoryEntry(ByVal DEObject As DirectoryEntry) As String
      Dim bytes As Byte() = CType(DEObject.Properties("objectSid").Value, Byte())
      Dim sid As New System.Security.Principal.SecurityIdentifier(bytes, 0)
      Return sid.ToString
End Function