Вы можете сделать это с пространством имен System.DirectoryServices.
Dim entry As DirectoryServices.DirectoryEntry
Dim mySearcher As System.DirectoryServices.DirectorySearcher
Dim result As System.DirectoryServices.SearchResult
Dim myEntry As DirectoryEntry
Dim domainName As String
Dim userId As String
Dim objectGuid As Guid
'Split the username into domain and userid parts
domainName = Page.User.Identity.Name.Substring(0, Page.User.Identity.Name.IndexOf("\"))
userId = Page.User.Identity.Name.Substring(Page.User.Identity.Name.IndexOf("\") + 1)
'Start at the top level domain
entry = New DirectoryEntry(domainName)
mySearcher = New DirectorySearcher(entry)
'Build a filter for just the user
mySearcher.Filter = ("(&(anr=" & userId & ")(objectClass=user))")
'Get the search result ...
result = mySearcher.FindOne
'... and then get the AD entry that goes with it
myEntry = result.GetDirectoryEntry
'The Guid property is the objectGuid
objectGuid = myEntry.Guid
Возможно, есть лучший способ сделать это, но это работает!