Which annotation allows a request to be executed with another Principal's identity?

C.

The correct answer is B. @UseIdentity.

Explanation: In Java EE, the @UseIdentity annotation can be used to allow a request to be executed with another Principal's identity. This annotation is used in conjunction with the runAs method of the EJBContext interface. The runAs method can be called to switch the identity of the current thread to the identity of the specified user.

For example, consider the following code snippet:

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@Stateless public class MyService {      @Resource     private EJBContext context;      @RolesAllowed({"admin"})     public void doAdminTask() {         // perform administrative task     }      @UseIdentity     public void doTaskAsUser(String username) {         context.getCallerPrincipal(); // returns the principal of the calling user         context.getEJBContext().runAs(username);         context.getCallerPrincipal(); // returns the principal of the specified user         doAdminTask(); // execute task as the specified user     }  } 

In this example, the doTaskAsUser method is annotated with @UseIdentity. This allows the method to execute with the identity of the specified user, rather than the identity of the calling user. The runAs method is used to switch the identity of the current thread to the specified user, and the doAdminTask method is then executed with the identity of the specified user.

Note that the @RolesAllowed annotation is used to restrict access to the doAdminTask method to users with the "admin" role. This annotation is not related to switching the identity of the current thread.

Option A, "It is not possible to execute a request with another Principal's identity," is incorrect because it is possible to do so using the @UseIdentity annotation and the runAs method.

Option C, @RolesAllowed, is incorrect because it is not related to switching the identity of the current thread.

Option D, @Runs, is not a valid annotation in Java EE.