XACML is dead
Conversations with vendors and IT end users at Forrester's Security lead us to predict that XACML (the lingua franca for centralized entitlement management and authorization policy evaluation and enforcement) is largely dead or will be transformed into access control (see Quest APS, a legacy entititlement management platform based on BiTKOO, which will probably be morphed by Dell into a web SSO platform).
Here are the reasons why we predict XACML is dead:
Lack of broad adoption. The standard is still not widely adopted with large enterprises who have written their authorization engines.
Inability to serve the federated, extended enterprise. XACML was designed to meet the authorization needs of the monolithic enterprise where all users are managed centrally in AD. This is clearly not the case today: companies increasingly have to deal with users whose identities they do not manage.
PDP does a lot of complex things that it does not inform the PEP about. If you get a 'no, you can't do that' decision in the application from the PEP, you'd want to know why. Our customers tell us that this can prove to be very difficult. The PEP may not be able to find out from the complex PDP evaluation process why an authorization was denied.
Not suitable for cloud and distributed deployment. While some PEPs can bundle the PDP for faster performance, using a PEPs in a cloud environment where you only have a WAN link between a PDP and a PEP is not an option.
Commercial support is non-existent. There is no software library with PEP support. Major ISVs have not implemented externalized authorization or plugin frameworks for externalized authorization. Replacing native SharePoint authorization with an Entitlement Management PEP is a nightmare requiring a one-off, non-standard, non-repeatable development and operations process.
Refactoring and rebuilding existing in-house applications is not an option. Entitlement Management deployment requires a refactoring of the application to use the PEP hooks for centralized, externalized authorization. This is not a reality at most companies. They cannot just refactor applications because of a different authorization model (sometimes, especially with mainframe applications the authorization model is not even understood well enough to do this…)
OAuth supports the mobile application endpoint in a lightweight manner. XACML today largely supports web based applications. While OAuth's current profiles are not a full-blown replacement for XACML functionality, we see that OAuth's simplicity made it the de-facto choice for mobile and also non-mobile applications.