The Rules of AD FS Claims Rules

Many people think of AD FS as merely a federated authentication service. And with a name like Active Directory Federation Services, it’s easy to see why. However, it also has the capacity to make authorisation decisions within its Claims Engine. This may be most familiar as the Office 365 Client Access Policies, but those policies are basically just a flavour of AD FS Issuance Authorisation Rules. An AD FS Issuance Authorisation rule provides a gate at AD FS, where permissions can be granted or denied to authentic users, per-Relying Party, before giving the user Claims for the requested Relying Party. In most cases we will think about these rules as coarse controls, to block a wide category of requests, such as those originating from outside the network, for members of a group, or for any combination of request-based, device-based and user attribute-based Claims. We can even create authorisation rules based on the user’s Identity Provider, or from additional factors of authentication. We will typically still implement most of our authorisation logic within the Relying Parties we are authenticating to, but in some cases it’s very useful to control access at this intermediary tier – especially if a large class of users, devices or networks should be treated as higher risk.

These concepts are not new, and the TechNet documentation I reference here dates back to the earliest wave of AD FS 2.0 RTW content:

Ultimately, I think these articles do answer the question of how to create an AD FS Issuance Authorisation rule, but I can’t point very clearly to the place on these pages that spells it out, and I do think there is a lot of confusing information about this in other places which may lead people astray. Namely, there is a lot of information that only concerns itself with the default Active Directory Claims Provider Rules and the Claims that come from request headers. Also, some of the most referenced AD FS + SharePoint content seems to have been written without authorisation rules in-mind. I want to try to clear some of that up in this post.

UPDATE 24/2/2015
I’ve added a fairly significant update regarding the new MFA stage in the pipeline half-way down this post.

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