Port over SecurityTokenProviders and consider replacing APM async model with "async"

Currently, in desktop, `SecurityTokenProvider` implements async with APM (i.e., `BeginXXX/EndXXX` methods). We should consider changing these out in favour of using `async` methods.

This will benefit long-term development as it will allow us to advantage of the `async` niceness and not have to handle Begin/End methods and the associated AsyncResults.

However, while going from APM to async probably will simplify the code a lot, it will likely be a lot of work to replumb all the calls into the various SecurityTokenProviders.

So this issue is essentially two-part:
- Bring over the necessary token providers for WCF client
- While doing so, consider whether or not we should move to `async` from `BeginXXX/EndXXX`