I still haven't found a better solution.
It would be really nice if the API could provide some functionality to just ask a service if the current user is authorized to see it or not.
But one thought that crossed my mind is that when you look at the services in the service directory, you don't see any information about service that your not authorized to see, they're just not there. So maybe you can't check if your authorized when the service, to that unauthorized user, doesn't seems to exist.