REP-1271 Implement Delegation in Client AuthN

So the only thing I don't like about this change is that the message is not very descriptive. Unfortunately, to provide a more descriptive message I would have to spend a fair amount of time refactoring the authentication filter. Options there include returning an object that includes a message, using ThreadLocal, or refactoring the code to be less distributed so that setting the header alongside the status code makes sense.

I also did not run the system test suite locally, so some of those may not pass. Let's find out!
Nope, it's just being used to pass some double in case the delegating element is not present. The double will never be used if we're not in delegating mode. I wish we had Options in Java, as that would be much cleaner.

I suppose we could just stick the result of the .getDelegating() call into the Configurable objects, but that means null checks later. Ew.