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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 to manage.
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 integrate with AsyncContext.start(Runnable)
and Spring MVC Async Integration.
DelegatingSecurityContextRunnable
One of the most fundamental building blocks within Spring Security’s concurrency support is the DelegatingSecurityContextRunnable
.
It wraps a delegate Runnable
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 <global-method-security>
support to secure one of your services.
You can now transfer the SecurityContext
of the current Thread
to the Thread
that invokes the secured service.
The following example show how you might do so:
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 preceding code:
-
Creates a
Runnable
that invokes our secured service. Note that it is not aware of Spring Security. -
Obtains the
SecurityContext
that we wish to use from theSecurityContextHolder
and initializes theDelegatingSecurityContextRunnable
. -
Uses the
DelegatingSecurityContextRunnable
to create aThread
. -
Starts the
Thread
we created.
Since it is common to create a DelegatingSecurityContextRunnable
with the SecurityContext
from the SecurityContextHolder
, there is a shortcut constructor for it.
The following code has the same effect as the preceding code:
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.
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 to use it.
Now we look at how DelegatingSecurityContextExecutor
can shield our code from any knowledge that we are using Spring Security.
The design of DelegatingSecurityContextExecutor
is similar to that of DelegatingSecurityContextRunnable
, except that it accepts a delegate Executor
instead of a delegate Runnable
.
The following example shows how to use it:
SecurityContext context = SecurityContextHolder.createEmptyContext();
Authentication authentication =
UsernamePasswordAuthenticationToken.authenticated("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);
This code:
Note that, in this example, we create the SecurityContext
by hand.
However, it does not matter where or how we get the SecurityContext
(for example, we could obtain it from the SecurityContextHolder
).
* Creates a delegateExecutor
that is in charge of executing submitted Runnable
objects.
* 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 case, the same SecurityContext
is used for every Runnable
submitted to our DelegatingSecurityContextExecutor
.
This is nice if we run background tasks that need to be run by a user with elevated privileges.
* At this point, you may ask 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
.
Consider the following example:
@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
, the originalRunnable
is run, and the SecurityContextHolder
is cleared out.
In this example, the same user is being used to run each thread.
What if we wanted to use the user from SecurityContextHolder
(that is, the currently logged in-user) at the time we invoked executor.execute(Runnable)
to process originalRunnable
?
You can do so by removing the SecurityContext
argument from our DelegatingSecurityContextExecutor
constructor:
SimpleAsyncTaskExecutor delegateExecutor = new SimpleAsyncTaskExecutor();
DelegatingSecurityContextExecutor executor =
new DelegatingSecurityContextExecutor(delegateExecutor);
Now, any time executor.execute(Runnable)
is run, the SecurityContext
is first obtained by the SecurityContextHolder
and then that SecurityContext
is used to create our DelegatingSecurityContextRunnable
.
This means that we are running our Runnable
with the same user that was used to invoke the executor.execute(Runnable)
code.
Spring Security Concurrency Classes
See the Javadoc for additional integrations with both the Java concurrent APIs and the Spring Task abstractions. They are self-explanatory once you understand the previous code.