XCTestCase setUp once with async operation

I'm trying to write some unit tests for an iOS client that consumes a web service API. I want to use the actual service and not mock data.

Before all the tests can run I need to get a token to authenticate the user with. I'm trying to use the class setUp method in order to do that - but I'm not sure how to wait for the token to arrive before I continue with the rest of the tests (since all network calls are async).