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6.4.6 Using EJB programmatic security
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In effect, programmatic security provides direct access to the Principal as well as a convenient means to check the Principal s role in the code. Both of these functions are made available through the EJB context. We ll begin exploring
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Exploring EJB security
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programmatic security by redeveloping the bid-canceling scenario as a starting point. Listing 6.6 implements the scenario.
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Listing 6.6 Securing bid cancellation using programmatic security
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@Stateless public class BidManagerBean implements BidManager { @Resource SessionContext context; ... public void cancelBid(Bid bid, Item item) { if (!context.isCallerInRole("CSR")) { throw new SecurityException( "No permissions to cancel bid"); } ... } ... }
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Injects EJB context
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Checks authorization
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Throws exception on violation
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Listing 6.6 first injects the EJB context b. We use the isCallerInRole method of the EJBContext to see if the underlying authenticated principal has the CSR role C. If it does not, we throw a java.lang.SecurityException notifying the user about the authorization violation D. Otherwise, the bid cancellation method is allowed to proceed normally. We discuss both the security management related methods provided in the EJB context next, namely isCallerInRole and getCallerPrincipal. isCallerInRole and getCallerPrincipal Programmatic security is made up solely of the two previously mentioned security-related methods. The methods are defined in the javax.ejb.EJBContext interface as follows:
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public interface EJBContext { ... public java.security.Principal getCallerPrincipal(); public boolean isCallerInRole(java.lang.String roleName); ... }
You ve already seen the isCallerInRole method in action; it is fairly selfexplanatory. Behind the scenes, the EJB context retrieves the Principal associated with the current thread and checks if any of its roles match the name you provided. The getCallerPrincipal method gives you direct access to the java. security.Principal representing the current authentication context. The only
Transactions and security
method of interest in the Principal interface is getName, which returns the name of the Principal. Most of the time, the name of the Principal is the login name of the validated user. This means that just as in the case of a homemade security framework, you could validate the individual user if you needed to. For example, let s assume that we had a change of heart and decided that in addition to the CSRs, bidders can cancel their own bids as long as the cancellation is done within a minute of putting in the bid. We could implement this using the getCallerPrincipal method as follows:
public void cancelBid(Bid bid, Item item) { if (!context.isCallerInRole("CSR") && !(context.getCallerPrincipal().getName().equals( bid.getBidder().getUsername()) && (bid.getTimestamp() >= (getCurrentTime() - 60*1000))))) { throw new SecurityException( "No permissions to cancel bid"); } ... }
Note, though, that there is no guarantee exactly what the Principal name might return. In some environments, it can return the role name, group name, or any other arbitrary String that makes sense for the authentication system. Before you use the Principal.getName method, you should check the documentation of your particular security environment. As you can see, the one great drawback of programmatic security management is the intermixing of security code with business logic as well as the potential hard-coding of role and Principal names. In previous versions of EJB, there was no way of getting around these shortfalls. However, in EJB 3 you can alleviate this problem somewhat by using interceptors. Let s see how to accomplish this next. Using interceptors for programmatic security As you know, in EJB 3 you can set up interceptors that are invoked before and after (around) any EJB business method. This facility is ideal for crosscutting concerns that should not be duplicated in every method, such as programmatic security (discussed in chapter 5) . We could reimplement listing 6.6 using interceptors instead of hard-coding security in the business method (see listing 6.7).
Listing 6.7 Using interceptors with programmatic security
public class SecurityInterceptor { Marks intercepted invocation @AroundInvoke public Object checkUserRole(InvocationContext context)
Summary
throws Exception { if (!context.getEJBContext().isCallerInRole("CSR")) { throw new SecurityException( Accesses "No permissions to cancel bid"); EJBContext from } InvocationContext return context.proceed(); } }
Specifies interceptor @Stateless for method public class BidManagerBean implements BidManager { @Interceptors(actionbazaar.security.SecurityInterceptor.class) public void cancelBid(Bid bid, Item item) { ... }
The SecurityInterceptor class method checkUserRole is designated as AroundInvoke, meaning it would be invoked whenever a method is intercepted b. In the method, we check to see if the Principal is a CSR C. If the role is not correct, we throw a SecurityException. Our BidManagerBean, on the other hand, specifies the SecurityInterceptor class as the interceptor for the cancelBid method D. Note that although using interceptors helps matters a bit in terms of removing hard-coding from business logic, there is no escaping the fact that there is still a lot of hard-coding going on in the interceptors themselves. Moreover, unless you re using a simple security scheme where most EJB methods have similar authorization rules and you can reuse a small number of interceptors across the application, things could become complicated very quickly. In effect, you d have to resort to writing ad hoc interceptors for method-specific authentication combinations (just admin, CSR and admin, everyone, no one, and so on). Contrast this to the relatively simple approach of using the declarative security management annotations or deployment descriptors. All in all, declarative security management is the scheme you should stick with, unless you have an absolutely unavoidable reason not to do so.
6.5 Summary
In this chapter, we discussed the basic theory of transactions, transaction management using CMT and BMT, basic security concepts, as well as programmatic and declarative security management. Both transactions and security are crosscutting concerns that ideally should not be interleaved with business logic. The EJB 3 take on security and transaction management tries to reflect exactly this belief, fairly successfully in our opinion, while allowing some flexibility.
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