If Service Desk is using OS Authentication (assuming a Windows server), when you try to log in to Service Desk, this is the authentication path that is followed:
- If the login ID is a local account (on the server) then the password is verified against the one on that local account (it is very rare that you would be using a local account).
- Then Windows checks to see if the login ID is in the Active Directory Domain to which the Service Desk server is associated. If so, then credentials are verified there.
- Then Windows checks trusted AD Domains to see if the login ID can be found there.
Note that the authentication path stops when a matching login ID is found. If the same login ID is in more than one domain then the authentication tries to use the first one it finds.