36. Concurrency Support

In most environments, Security is stored on a per Thread basis. This means that when work is done on a new Thread , the SecurityContext is lost. Spring Security provides some infrastructure to help make this much easier for users. Spring Security provides low level abstractions for working with Spring Security in multi-threaded environments. In fact, this is what Spring Security builds on to integration with Section 15.2.4, “AsyncContext.start(Runnable)” and Section 37.4, “Spring MVC Async Integration”.

36.1 DelegatingSecurityContextRunnable

One of the most fundamental building blocks within Spring Security’s concurrency support is the DelegatingSecurityContextRunnable . It wraps a delegate Runnable in order to initialize the SecurityContextHolder with a specified SecurityContext for the delegate. It then invokes the delegate Runnable ensuring to clear the SecurityContextHolder afterwards. The DelegatingSecurityContextRunnable looks something like this:

public void run() {
try {
	SecurityContextHolder.setContext(securityContext);
	delegate.run();
} finally {
	SecurityContextHolder.clearContext();
}
}

While very simple, it makes it seamless to transfer the SecurityContext from one Thread to another. This is important since, in most cases, the SecurityContextHolder acts on a per Thread basis. For example, you might have used Spring Security’s Section 41.4.1, “<global-method-security>” support to secure one of your services. You can now easily transfer the SecurityContext of the current Thread to the Thread that invokes the secured service. An example of how you might do this can be found below:

Runnable originalRunnable = new Runnable() {
public void run() {
	// invoke secured service
}
};

SecurityContext context = SecurityContextHolder.getContext();
DelegatingSecurityContextRunnable wrappedRunnable =
	new DelegatingSecurityContextRunnable(originalRunnable, context);

new Thread(wrappedRunnable).start();

The code above performs the following steps:

  • Creates a Runnable that will be invoking our secured service. Notice that it is not aware of Spring Security

  • Obtains the SecurityContext that we wish to use from the SecurityContextHolder and initializes the DelegatingSecurityContextRunnable

  • Use the DelegatingSecurityContextRunnable to create a Thread

  • Start the Thread we created

Since it is quite common to create a DelegatingSecurityContextRunnable with the SecurityContext from the SecurityContextHolder there is a shortcut constructor for it. The following code is the same as the code above:

Runnable originalRunnable = new Runnable() {
public void run() {
	// invoke secured service
}
};

DelegatingSecurityContextRunnable wrappedRunnable =
	new DelegatingSecurityContextRunnable(originalRunnable);

new Thread(wrappedRunnable).start();

The code we have is simple to use, but it still requires knowledge that we are using Spring Security. In the next section we will take a look at how we can utilize DelegatingSecurityContextExecutor to hide the fact that we are using Spring Security.

36.2 DelegatingSecurityContextExecutor

In the previous section we found that it was easy to use the DelegatingSecurityContextRunnable , but it was not ideal since we had to be aware of Spring Security in order to use it. Let’s take a look at how DelegatingSecurityContextExecutor can shield our code from any knowledge that we are using Spring Security.

The design of DelegatingSecurityContextExecutor is very similar to that of DelegatingSecurityContextRunnable except it accepts a delegate Executor instead of a delegate Runnable . You can see an example of how it might be used below:

SecurityContext context = SecurityContextHolder.createEmptyContext();
Authentication authentication =
	new UsernamePasswordAuthenticationToken("user","doesnotmatter", AuthorityUtils.createAuthorityList("ROLE_USER"));
context.setAuthentication(authentication);

SimpleAsyncTaskExecutor delegateExecutor =
	new SimpleAsyncTaskExecutor();
DelegatingSecurityContextExecutor executor =
	new DelegatingSecurityContextExecutor(delegateExecutor, context);

Runnable originalRunnable = new Runnable() {
public void run() {
	// invoke secured service
}
};

executor.execute(originalRunnable);

The code performs the following steps:

  • Creates the SecurityContext to be used for our DelegatingSecurityContextExecutor . Note that in this example we simply create the SecurityContext by hand. However, it does not matter where or how we get the SecurityContext (i.e. we could obtain it from the SecurityContextHolder if we wanted).

  • Creates a delegateExecutor that is in charge of executing submitted Runnable s

  • Finally we create a DelegatingSecurityContextExecutor which is in charge of wrapping any Runnable that is passed into the execute method with a DelegatingSecurityContextRunnable . It then passes the wrapped Runnable to the delegateExecutor. In this instance, the same SecurityContext will be used for every Runnable submitted to our DelegatingSecurityContextExecutor . This is nice if we are running background tasks that need to be run by a user with elevated privileges.

  • At this point you may be asking yourself "How does this shield my code of any knowledge of Spring Security?" Instead of creating the SecurityContext and the DelegatingSecurityContextExecutor in our own code, we can inject an already initialized instance of DelegatingSecurityContextExecutor .

@Autowired
private Executor executor; // becomes an instance of our DelegatingSecurityContextExecutor

public void submitRunnable() {
Runnable originalRunnable = new Runnable() {
	public void run() {
	// invoke secured service
	}
};
executor.execute(originalRunnable);
}

Now our code is unaware that the SecurityContext is being propagated to the Thread , then the originalRunnable is executed, and then the SecurityContextHolder is cleared out. In this example, the same user is being used to execute each Thread. What if we wanted to use the user from SecurityContextHolder at the time we invoked executor.execute(Runnable) (i.e. the currently logged in user) to process originalRunnable ? This can be done by removing the SecurityContext argument from our DelegatingSecurityContextExecutor constructor. For example:

SimpleAsyncTaskExecutor delegateExecutor = new SimpleAsyncTaskExecutor();
DelegatingSecurityContextExecutor executor =
	new DelegatingSecurityContextExecutor(delegateExecutor);

Now anytime executor.execute(Runnable) is executed the SecurityContext is first obtained by the SecurityContextHolder and then that SecurityContext is used to create our DelegatingSecurityContextRunnable . This means that we are executing our Runnable with the same user that was used to invoke the executor.execute(Runnable) code.

36.3 Spring Security Concurrency Classes

Refer to the Javadoc for additional integrations with both the Java concurrent APIs and the Spring Task abstractions. They are quite self-explanatory once you understand the previous code.

  • DelegatingSecurityContextCallable

  • DelegatingSecurityContextExecutor

  • DelegatingSecurityContextExecutorService

  • DelegatingSecurityContextRunnable

  • DelegatingSecurityContextScheduledExecutorService

  • DelegatingSecurityContextSchedulingTaskExecutor

  • DelegatingSecurityContextAsyncTaskExecutor

  • DelegatingSecurityContextTaskExecutor