matching password from client with password in AD - asp.net

Question

the code I have below works, but it doesn't use the password that is passed from the client. After I find the correct user in the AD, is there a way to match the password that is passed from the client with the password in the AD?
Thanks!
Public Class FordLoginController
Inherits ApiController
Public Class StoreCredentials
Public Property UsernameAX As String
Public Property PasswordAX As String
End Class
Public Function PostValue(<FromBody()> ByVal creds As StoreCredentials) As HttpResponseMessage
Dim username As String = creds.UsernameAX
Dim password As String = creds.PasswordAX
Dim ctx As New PrincipalContext(ContextType.Domain, "ford", "dc=biz,dc=ford,dc=com")
Dim user As UserPrincipal = UserPrincipal.FindByIdentity(ctx, username)
Dim response As HttpResponseMessage
If user IsNot Nothing Then
response = Request.CreateResponse(HttpStatusCode.Found)
response.Headers.Location = New Uri("/loginAndContinue/login.aspx")
Return response
End If
response = Request.CreateResponse(HttpStatusCode.Forbidden)
Return response
End Function
End Class

Answer 1

From VBForums
http://www.vbforums.com/showthread.php?352349-Validate-Login-against-Active-Directory
Private Function ValidateActiveDirectoryLogin(ByVal Domain As String, ByVal Username As String, ByVal Password As String) As Boolean
Dim Success As Boolean = False
Dim Entry As New System.DirectoryServices.DirectoryEntry("LDAP://" & Domain, Username, Password)
Dim Searcher As New System.DirectoryServices.DirectorySearcher(Entry)
Searcher.SearchScope = DirectoryServices.SearchScope.OneLevel
Try
Dim Results As System.DirectoryServices.SearchResult = Searcher.FindOne
Success = Not (Results Is Nothing)
Catch
Success = False
End Try
Return Success
End Function
usage
If ValidateActiveDirectoryLogin("VBForums", "Woof", "Mouse") Then
'do something
End If