Silverlight™ 3 Programmer's Reference

Chapter 13. First Things First: Handling Cross-Cutting Concerns

Cross-cutting concerns are those system design issues that cut across the various areas of an application and are typically foundational system services that you need to consider before diving into building an application. Most common among these are security, exception handling, and logging. In this chapter, you'll get an understanding of how to address these in your applications, particularly how these concerns change in the context of a Silverlight application.

Security

In this section, you'll look at the various aspects of security that you'll need to think about for Silverlight applications.

Code Access Security Model

Silverlight 3 completely rips out the familiar .NET Code Access Security (CAS) model and replaces it with a straightforward, invisible model. Because it is targeted strictly at web applications and runs in the browser, it more or less inherits the browser/AJAX security model in terms of what it allows applications to do. So, in a sense, the burden of security, particularly code security, is removed from the developer — no worrying about attributes, asserts, demands, and that sort of thing.

Under the covers it is more complicated than that, of course. Platform (Microsoft) code has the ability to do things that aren't what you'd call sandboxed, things like accessing the host filesystem. To do this, Silverlight has essentially three layers of security. The first is the transparent, which is where your application ...