Monday, August 20, 2012
XACML and the SDLC (Architecture and Design): Part One
JM: Historically speaking, a majority of enterprise applications were built without regard to modern approaches to either identity or entitlements management. At the same time, there is no published guidance by either the information security community or industry analysts in terms of how not to repeat past sins. So, let’s dive into some of the challenges a security architecture team should consider when providing guidance to developers on building applications securely. Are you game?
GG: Definitely! I think it remains an issue that applications are still being built without a modern approach to identity or entitlements – we see many cases where developers make their own determinations on how to best handle these tasks. Security architects and enterprise architects have long professed the desire to externalize security and identity from applications, but this guidance has an uneven track record of success.
JM: The average enterprise is not short of places to store identity. One common place where identity is stored is within Active Directory. However, infrastructure teams generally don’t allow for extending Active Directory for application purposes. So, should architects champion having a separate identity store for enterprise applications or somehow find a way to at least centralize application identity?
GG: Attribute management and governance is a key element to an ABAC (attribute based access control) approach. You might expect that one source of identity data is ideal, but that is not the reality of most deployments. Identity and other attribute data is distributed between AD, enterprise directories, HR, databases, CRM systems, supply chain systems, etc. The important thing is to have a process for policy modeling that is aware of and accommodates the source of attributes that are used in decision making.
For example, some attributes are derived from the session and application context, captured by the policy enforcement point (PEP) code and sent to the policy decision point (PDP) with the access request. The PDP can look up additional attributes through a policy information point (PIP) interface. The PIP is configured to connect with authoritative sources of information, which could be additional information about the user, resource or environment.
JM: While I haven’t ran across an enterprise that has gotten a handle on identity, I can also say that many security architecture professionals haven’t figured out ways to stitch together identity on the fly either. If we are going to leave identity distributed, what should we consider?
GG: I am a proponent of a distributed model as the starting point for this issue. That is, identity data should be stored and managed in close proximity to its authoritative source. In a distributed approach such as this, data accuracy should be better than if it is synchronized into a central source. Others will argue for data synchronization, and it is important when performance requirements call for a local copy of data. Therefore, performance, latency and data volatility are all issues to consider.
JM: What if an enterprise application currently assumes that authentication occurs by taking a user-provided token and compares it to something stored within the applications database. Many shops deploy web access management (WAM) technologies such as Yale CAS, CA Siteminder, etc where they centralize authentication and pass around session cookies but may not to know from an identity perspective why this may not be a complete solution?
GG: A few things come to mind here. First, a WAM session token is proprietary and therefore has a number of limitations in the areas of interoperability, support in multiple platforms, etc.
Second, there is the issue of separation of concerns. From an architectural perspective, I strongly believe in having an approach that treats authentication separate from authorization concerns. One of the main benefits is the ability to adjust your authentication scheme to meet the rapidly changing threats that we see emerging on a daily or weekly basis. If authentication is tightly coupled with another identity component, then an organization is severely limiting its ability to cope with security threats.
Finally, authentication should be performed at the identity domain that is most familiar with the user. Said another way, each application does not and should not store a credential for users. Federation standards permit the user to authenticate at their home domain and present a standardized token to applications they may subsequently access.
JM: Have you ever been to a website where they ask you to enter your credentials and they don’t provide you with any queues as to what form the credential comes in? For example is it a User ID or email address. A person may have multiple unique identifiers. Is it possible to use entitlements management as a centralized authenticator for an enterprise application in this scenario?
GG: My initial thought is “no” based on my comments regarding separating authN and authZ above. There are also security reasons for not giving the user a hint about the credential – to reduce the attack surface for someone trying to compromise the site.
However, there may be cases where a web site wishes to permit the use of multiple unique identifiers for authentication. Once you get to the authorization step, will you still have all the necessary user attributes available? Do you need to map all the identifiers to the attribute stores? You can end up making the authorization more complex than it needs to be.
JM: If you have ever witnessed how enterprise applications are developed, they usually start out with the notion of two roles where the first role is a user and the second is the administrator. The user can do a few things and the administrator can do anything. Surely, we need to have something more finer-grained than this if we want to improve the security of enterprise applications. What guidance could you provide in terms of modeling roles?
GG: There are different levels of roles that should be defined for any given application:
- Security Administrator: Their only purpose is to manage and potentially assign entitlements.
- System Administrator: They just manage the application or platform but don’t deal with entitlements
- User Role: Here are the regular users that will interact with the system
Third, you can define a user role that permits an individual to login to the application but with very limited capabilities. Here is where ABAC/XACML comes in to give you the granularity required. Access rules can define what functions a user role can perform as well as what data they can perform functions on. With this kind of dynamic capability, you can enforce rules such as, Managers can view payroll data for employees in their department.
JM: I had the opportunity in my career to be the lead architect for many once popular and now defunct Internet startups during the dot-com era. At no time, do I remember anyone ever inquiring about a standard around what a resource naming convention should look like. Even today, many enterprise applications have no discernable standards as to what a URL should look like. Now that we have portals and web services, this challenge is even more elusive. I know that web access management technologies use introspection techniques and therefore are suboptimal in this regard. Does Entitlements Management provide a potential solution and if so, what constructs should we consider in designing new enterprise applications?
GG: The XACML policy language includes a namespace and naming convention for attributes, policies, etc. This helps to organize the system and also to avoid conflicts in the use of metadata. It is also possible to incorporate semantic web approaches or ontologies to manage large and complex environments – we are seeing some customers interested in exploring these capabilities.
JM: I have heard Gunnar Peterson use an analogy in a testing context that makes me smile. He once stated, testing through the UI is like attempting to inspect the plumbing in your basement by peering through your showerhead. This seems to hint that many applications think of security only through the user interface. Does entitlements management provide the ability to define a security model that is cohesive and deals with all layers of an enterprise application?
GG: Absolutely, this is one of the strengths of the XACML architecture. You can define all the access rules that an XACML policy server will enforce – and install policy enforcement points (PEP) at the necessary layers of an application. These are typically installed at the presentation, application and data tiers or layers. Such an approach is important because you have a different session context at each layer and may have different security concerns to address, but the organization needs to ensure that a set of access rules are consistently enforced throughout the layers of the application. Further, individual services or APIs can be secured as they are used on their own or in mash-up scenarios.
You get the additional benefit of a consolidated access log for all layers of the application. All access successes and failures are available for reporting, investigations or forensic purposes.
JM: Some enterprises are moving away from thinking in terms of objects towards thinking in terms of business processes. How should a security architect think about applying an entitlements-based approach to BPM?
GG: I recall writing some years ago that BPM tools could facilitate the creation of application roles – it’s very interesting that you now ask me about BPM and entitlements! But it’s a logical question. BPM tools help you map out and visualize the application, have the notion of a namespace, resources, and so on. At least a couple of places where entitlements and authorization rules can be derived are within BPM activities as well as when you have an interaction with an activity in another swim lane.
JM: Enterprises are also developing mobile applications that allow their consumers to access services, pay bills and conduct business transactions. It goes without saying that a mobile application should have the same security model or at least adhere to the same security principles as an internally hosted web application. What are some of the entitlements considerations an architect should think about?
GG: There are several considerations that come to mind, but let’s address just a few of them here.
- Do you need to limit functionality or data download for mobile devices? This can be enforced in your access policies.
- Do you need to control what functions/buttons/content is displayed on the screen? This is commonly done for access via non-mobile browsers.
- Do you need to support offline mode or deal with low bandwidth connections (insert your least favorite carrier here). In this case, you may need to support long-lived entitlements or access decisions as opposed to the normal transactional model for XACML systems.
- Where is the data? How much data is stored on the mobile device? Is the data stored in the cloud? The answers to these questions help to determine how the authorization solution is architected.
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