25. Secure Object Implementations
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## 25. Secure Object Implementations

## 25.1 AOP Alliance (MethodInvocation) Security Interceptor

Prior to Spring Security 2.0, securing `MethodInvocation` s needed quite a lot of boiler plate configuration. Now the recommended approach for method security is to use namespace configuration. This way the method security infrastructure beans are configured automatically for you so you don’t really need to know about the implementation classes. We’ll just provide a quick overview of the classes that are involved here.

Method security in enforced using a `MethodSecurityInterceptor`, which secures `MethodInvocation` s. Depending on the configuration approach, an interceptor may be specific to a single bean or shared between multiple beans. The interceptor uses a `MethodSecurityMetadataSource` instance to obtain the configuration attributes that apply to a particular method invocation. `MapBasedMethodSecurityMetadataSource` is used to store configuration attributes keyed by method names (which can be wildcarded) and will be used internally when the attributes are defined in the application context using the `<intercept-methods>` or `<protect-point>` elements. Other implementations will be used to handle annotation-based configuration.

### 25.1.1 Explicit MethodSecurityInterceptor Configuration

You can of course configure a `MethodSecurityIterceptor` directly in your application context for use with one of Spring AOP’s proxying mechanisms:

    <bean id="bankManagerSecurity" class=
    	"org.springframework.security.access.intercept.aopalliance.MethodSecurityInterceptor">
    <property name="authenticationManager" ref="authenticationManager"/>
    <property name="accessDecisionManager" ref="accessDecisionManager"/>
    <property name="afterInvocationManager" ref="afterInvocationManager"/>
    <property name="securityMetadataSource">
    	<sec:method-security-metadata-source>
    	<sec:protect method="com.mycompany.BankManager.delete*" access="ROLE_SUPERVISOR"/>
    	<sec:protect method="com.mycompany.BankManager.getBalance" access="ROLE_TELLER,ROLE_SUPERVISOR"/>
    	</sec:method-security-metadata-source>
    </property>
    </bean>

## 25.2 AspectJ (JoinPoint) Security Interceptor

The AspectJ security interceptor is very similar to the AOP Alliance security interceptor discussed in the previous section. Indeed we will only discuss the differences in this section.

The AspectJ interceptor is named `AspectJSecurityInterceptor`. Unlike the AOP Alliance security interceptor, which relies on the Spring application context to weave in the security interceptor via proxying, the `AspectJSecurityInterceptor` is weaved in via the AspectJ compiler. It would not be uncommon to use both types of security interceptors in the same application, with `AspectJSecurityInterceptor` being used for domain object instance security and the AOP Alliance `MethodSecurityInterceptor` being used for services layer security.

Let’s first consider how the `AspectJSecurityInterceptor` is configured in the Spring application context:

    <bean id="bankManagerSecurity" class=
    	"org.springframework.security.access.intercept.aspectj.AspectJMethodSecurityInterceptor">
    <property name="authenticationManager" ref="authenticationManager"/>
    <property name="accessDecisionManager" ref="accessDecisionManager"/>
    <property name="afterInvocationManager" ref="afterInvocationManager"/>
    <property name="securityMetadataSource">
    	<sec:method-security-metadata-source>
    	<sec:protect method="com.mycompany.BankManager.delete*" access="ROLE_SUPERVISOR"/>
    	<sec:protect method="com.mycompany.BankManager.getBalance" access="ROLE_TELLER,ROLE_SUPERVISOR"/>
    	</sec:method-security-metadata-source>
    </property>
    </bean>

As you can see, aside from the class name, the `AspectJSecurityInterceptor` is exactly the same as the AOP Alliance security interceptor. Indeed the two interceptors can share the same `securityMetadataSource`, as the `SecurityMetadataSource` works with `java.lang.reflect.Method` s rather than an AOP library-specific class. Of course, your access decisions have access to the relevant AOP library-specific invocation (ie `MethodInvocation` or `JoinPoint`) and as such can consider a range of addition criteria when making access decisions (such as method arguments).

Next you’ll need to define an AspectJ `aspect`. For example:

    package org.springframework.security.samples.aspectj;

    import org.springframework.security.access.intercept.aspectj.AspectJSecurityInterceptor;
    import org.springframework.security.access.intercept.aspectj.AspectJCallback;
    import org.springframework.beans.factory.InitializingBean;

    public aspect DomainObjectInstanceSecurityAspect implements InitializingBean {

    	private AspectJSecurityInterceptor securityInterceptor;

    	pointcut domainObjectInstanceExecution(): target(PersistableEntity)
    		&& execution(public * *(..)) && !within(DomainObjectInstanceSecurityAspect);

    	Object around(): domainObjectInstanceExecution() {
    		if (this.securityInterceptor == null) {
    			return proceed();
    		}

    		AspectJCallback callback = new AspectJCallback() {
    			public Object proceedWithObject() {
    				return proceed();
    			}
    		};

    		return this.securityInterceptor.invoke(thisJoinPoint, callback);
    	}

    	public AspectJSecurityInterceptor getSecurityInterceptor() {
    		return securityInterceptor;
    	}

    	public void setSecurityInterceptor(AspectJSecurityInterceptor securityInterceptor) {
    		this.securityInterceptor = securityInterceptor;
    	}

    	public void afterPropertiesSet() throws Exception {
    		if (this.securityInterceptor == null)
    			throw new IllegalArgumentException("securityInterceptor required");
    		}
    	}
    }

In the above example, the security interceptor will be applied to every instance of `PersistableEntity`, which is an abstract class not shown (you can use any other class or `pointcut` expression you like). For those curious, `AspectJCallback` is needed because the `proceed();` statement has special meaning only within an `around()` body. The `AspectJSecurityInterceptor` calls this anonymous `AspectJCallback` class when it wants the target object to continue.

You will need to configure Spring to load the aspect and wire it with the `AspectJSecurityInterceptor`. A bean declaration which achieves this is shown below:

    <bean id="domainObjectInstanceSecurityAspect"
    	class="security.samples.aspectj.DomainObjectInstanceSecurityAspect"
    	factory-method="aspectOf">
    <property name="securityInterceptor" ref="bankManagerSecurity"/>
    </bean>

That’s it! Now you can create your beans from anywhere within your application, using whatever means you think fit (eg `new Person();`) and they will have the security interceptor applied.

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