Is “Code Access Security” of any real world use?

Question

Warning:

Newer versions of .Net and .Net core has have removed and/or changed “Code Access Security” (CAS) since this question was asked.

Original Questio

Answer 1

Note to reader: see the two comments below; it sounds like I'm accidentally inflating the definition of CAS to (incorrectly) include RBS. I'll leave the answer here for reference, but note the distinction.

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There are two havles to CAS; the thing you'll see most about in that exam is all the nuances for code calling other code, which may be useful for partial trust, but most of the time it is simply a pain - and worse: if your code has full trust (which most / too-much does) none of it actually executes (it is skipped entirely).

The useful part of CAS RBS is principal permission, which is used; of course, your UI should verify access to features, but you can put (in your low-down logic):

[PrincipalPermission(SecurityAction.Demand, Role = "ADMIN")]
static void DeleteOrder(int id) { ... }

This will be enforced even in full trust; you can define your own principal (tied to the user) by implementing IPrincipal (look at IsInRole()). And since principals are supported in most environments (winforms, webforms, mvc, wcf, etc) this can make for a very flexible way to double-check security at the business layer without having to reference the specific security model. Note that the above check would work in any environment.

You can also perhaps use this to drive your UI. I did have a usenet post that enabled / disabled winforms controls based on the principal (using runtime properties to specify the role per control, a bit like ToolTip etc) - I can't find it at the minute, though (edit: maybe this one).