[jboss-as7-dev] On security context and propagation

The Problem =========== In order to support all the Java EE 7 requirements, we need to be able to propagate security context in a predictable and uniform manner. Unfortunately, we have almost as many security context concepts as we do projects which support authentication. There is no single way to execute a task given a security context snapshot from another thread that will work for all of our projects. Project-Specific Security Context --------------------------------- The typical implementation of a project-specific security context is just a Subject, cached into a ThreadLocal and available via some accessors. In addition we have the SecurityRolesAssociation concept from PicketBox, which is meant to encapsulate roles from an EE perspective. Available Mechanisms ==================== A number of mechanisms are provided by the JDK and the EE SDK specifically for addressing this problem domain. Here's a quick review so we are all speaking the same language. javax.security.auth.Subject --------------------------- The focal point for security in both SE and EE is the Subject class, which is an encapsulation of related information for a security entity, including credentials (passwords, keys, etc.) and identities (user/group names, roles, etc.). Most (not all) of our security-aware projects already seem to use Subject, though they may not all be using it in the same way. Subject has some utility methods which are intended to allow association with the current security context. With these methods you can run tasks as different Subjects. We currently do not support these methods. java.security.Principal ----------------------- The base interface for an identity. Though there are no specific supported implementations for EE use cases, this interface would be the base for user names, group names, role names, and so on. JDK Principal implementations do exist for filesystem users and groups, certificate signers and principals, JMX authenticated identities, etc. java.security.AccessControlContext ("ACC") ------------------------------------------ This is *the* JDK-provided security context. It represents the accumulated privileges of "protection domains", which can in turn correspond to principals, permissions, and/or code sources (i.e. JARs). A given ACC, in simplified terms, represents the *intersection* of privileges granted by all the invocations on the call stack. It gets a bit complex once you plumb the depths but imagine ACC conceptually like a second execution stack. Every time you call into another module, you push another layer on the stack which includes that module's permission set (which is AllPermission by default, but can be restricted on a per-module basis). This also includes calling into deployments. You can also push a Subject on to this stack using Subject.doAs*(). It is worth emphasizing that the effective permission set for an ACC is the intersection of all of its parts, so the more calls you make, the more restricted your permissions are. This is why we use AccessController.doPrivileged*() and/or Subject.doAsPrivileged(): it "clears" the stack for the duration of the invocation, adding only the module which hosts the Privileged*Action class being executed (and optionally the given Subject as well). This becomes important when you consider that in many cases, you have no idea under what context a given piece of code will be run, thus you cannot be certain whether a restricted operation will succeed without using doPrivileged(). Perhaps the canonical case of this is class initialization. Common sense would seem to imply that classes should always be initialized in a privileged context, but that does not seem to be the case in reality. Thus class init is often stuck with awkward doPrivileged constructs, especially when field init is involved. A Unified Security Context ========================== The ACC affords us a uniquely suited mechanism for security association. Subjects are already designed to be connected into ACCs; in fact, you can query an ACC for its associated Subject with a simple get. In turn the Subject can be queried for its Principals and credentials. This also gives us saner integration with JAAS, to the extent that such sanity is possible; users can use the returned Subject with Subject.doAs() and get the results they would expect in any situation. Finally ACC is in the JDK - any third-party security-aware framework is much more likely to integrate with ACC and Subject than with some framework provided by us. And, the JDK security manager framework is ready to handle it, so a user security policy could for example forbid certain Subjects from performing operations as an additional security layer. Getting the Current Subject --------------------------- To get the current subject you can do something like this: Subject current = Subject.getSubject(AccessController.getContext()); This will work from any context - though there is a permission check involved so a security action is in order in this case. Propagation Within the AS ------------------------- We need to do in-system propagation of security context in a few situations. The predominant one (to me) is using JSR-236 thread pools - tasks submitted by an EE component must run under the same security context that the submitter holds. Fortunately propagation of this nature is quite simple: use AccessController.getContext() to acquire the current security context, and use AccessController.doPrivileged() to resume. Propagation to other components (e.g. EJBs) is a little different though. In this case you do not want the baggage of the caller ACC; you only need to preserve the caller Subject. In this case, you would acquire the Subject as above, and the security interceptor would simply use Subject.doAs() to resume. Propagation Over the Network ---------------------------- It should be possible to use Principal information stored on the Subject in combination with private credentials to provide all the information required for network propagation of security context. This should work particularly well with the Remoting authentication service in particular. One Step Farther: ACC-Based Permission Checking ----------------------------------------------- It is possible to take this idea a little farther and introduce permission checking for JACC-style permissions based on the ACC. Using ACC.checkPermission we can do permission checking regardless of the presence or absence of a SecurityManager. However, it is not clear what benefits we would derive from this move (if any). Costs and Alternatives ====================== ACC is not free. It's a fairly heavyweight structure (though it does make certain optimizations in some cases), and it contains what is probably more information than is strictly necessary as it is designed for full-bore SecurityManager sandboxing and permission checking. Thus it is worth exploring alternatives. Alternative: Central Security Context ------------------------------------- Alternative #1 is to support a central security context represented by a Subject in one place which all frameworks and libraries share. Pros: lightweight (as much as possible anyway); conceptually simple Cons: not compatible Subject.doAs or AccessController.doPrivileged; additional dependency for all security-aware frameworks; third-party stuff is less likely to just work Alternative: ??? ---------------- Add your ideas here! Action ====== I think, barring any major dissent, we should make a move towards using ACC as a unified security context. I think that given the EE 7 security manager requirements and user requests over time, that standardizing around ACC makes sense. Discussion: go! -- - DML