The following VBScript function can be used to check if a given username and password has access to the specified domain. It will return true or false depending on whether or not access was granted.
function fnCheckAccess(strDomain, strUserID, strUserPWD)
const ADS_SECURE_AUTHENTICATION = &H01
const ADS_CHASE_REFERRALS_ALWAYS = &H60
dim objDSO
dim objUser
dim strPath
strPath = "LDAP://" & strDomain
On Error Resume Next
set objDSO = GetObject("LDAP:")
set objUser = objDSO.OpenDSObject(strPath, strUserID, strUserPWD, ADS_SECURE_AUTHENTICATION OR ADS_CHASE_REFERRALS_ALWAYS)
if Err.Number <> 0 then
fnCheckAccess = False
else
fnCheckAccess = True
end if
Err.Clear
On Error Goto 0
set objDSO = Nothing
set objUser = Nothing
end function