Federated Authorization

For a while now the use of federated userids has been the norm. A site called the Service Provider, SP, has entered into agreement with another, called the Identity Provider, IP that it will trust the userid the IP sends it as being properly authenticated and accurately identifies the user.
There are a number of way this can be done; the passing of a SAML token from the IP to the SP is a popular way. Where the SAML token contains the userid and the SP trusts this because the token is signed by the IP.

So much for users and their userids, but what about what they have access to; The authorization.
Userids are tied to revenue in significant ways. In businesses deriving revenue from gathering information about the users, the useris is clearly of primary concern. More generally in business applications it is not the userid itself that is central, but what the user has access to and how to execute that access control.

In a standard access control deployment scenario with federated users. For example the user login somewhere else (the IP) and click a link to (return to ) the application in question, with the userid being passed along. This is a federated login. The application (the SP) still examines the userid and refers to its own access control infrastructure for what the user is authorized to do. Could this step be federated too ? Should it ?
Like a login and authentication infrastructure costs money, so does maintaining an access control infrastructure. Federated login cuts the costs of the first, so can Federated Authorization, FA, cut the second.
Form the cost point of view FA makes sense.

Can it be done and does it make sense from a policy and governance point of view ?. It is one thing to let someone else identify the user on your behalf. Digital certificates have been around for a while so the issues surrounding outsourcing the work of identify users are not new. And the risks are largely accepted. But authorization cuts close to the essentials of governance: what are people permitted to do. True, if the user is misidentified having a thorough access control system does not make much difference.
One significant issue is related to changes. A user ID doesn’t change much, if at all. What a user has access to, does. Sometimes great urgency. Having direct control of authorization is then desirable.

The day-to-day problem with access control is not primarily the enforcement, though that can be tricky enough. It is the creation of and updates to policy. The rules governing the access. Who gets to decide and how can those decisions be captured in an enforceable way.

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