Cross domain authentication

Christopher Ong
Christopher Ong used Ask the Experts™
Here is my scenario:

Users and workstations at site X authenticate to an AD under, let's say, Domain-X

The servers are hosted at a remote data centre, which has a domain named Domain-Y.

Now, the users need to access the web portals under Domain-Y. In this case, should I deploy an ADFS in the data centre perimeter network to handle the authentication requests? I've read up a bit on ADFS and it seems that it is not trivial to set this up.

In actual fact, the users, workstations and servers all belong to the same organization, and I want to keep things simple. I thought of setting up a one way trust from the server domain (Domain-Y) to the site X domain (Domain-Y). But in doing so, do I still need an ADFS?

Lastly, does the AD at Domain-Y need a connection to the AD at Domain-X to retrieve the user account info?

All help is much appreciated. Thanks in advance.
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ADFS is not trivial at all - excpet of course to ADFS experts.  Unfortunately, I am not one.  If however you have direct access to from Domain-X to Domain-Y (via site-to-site VPN for example), then you can probably get away with doing a regular trust relationship between the two domains - and then be able to grant permissions quite easily that way.

If Domain-X and Domain-Y are part of the same AD Forest, then you already have the trust set up.  With a trust, both Domain-X and Domain-Y need to be able to talk to each other.


What you've said confirmed my worst fears i.e. ADFS is not trivial. My issue is compounded by the fact that the data centre, being a third party, has imposed certain restrictions.

For one, they don't allow the AD at site X to talk to the AD at the data centre directly. Although there is site-to-site VPN between site X and the DC, it terminates at the perimeter network. The two domains are distinct, therefore they are in different forests which is why I need to set up an explicit trust. But as you have mentioned, a trust won't work if both ADs cannot talk to each other directly. That's what led me to think about ADFS.

What approach would you suggest to simplify deployment?
It seems that ADFS can be your solution in that case, because it's specifically designed to grant access to web applications based on tokens (Claims based authentication).

A good blog on how it works can be seen here: - and it contains a nice diagram entitled "ADFS Simplified"

Technet also provides deployment guides - available at

Unfortunately, that's as much help as I am able to give - I wish I had more ADFS experience myself.

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