Async in [BeforeClass]

I need to perform a log in in my [BeforeClass] method.  Unfortunately, this log in takes place Asynchronously outside of the test.  This results in the [Test] methods being performed before the [BeforeClass] has completed.  Is there a way I can wait on an event in the [BeforeClass] method before proceeding to the [Before] and [Test] methods?  Examples would be great, thanks!

-Andrew