Stripe card validation passed w/ iOS, failed in Rails

As a follow up to my recent post about weird cc verifications, Stripe returns a token when I pass a card with a valid number but invalid CVC & zip code. I checked "require CVC & zip code authentication" in the account settings in the dashboard.

I will receive an error from Stripe in my iOS app if I pass an invalid card number but a token if I have a valid card + valid CVC.

When I charge the card, Stripe errors on the server.

How do I authenticate the card immediately, without charging it? (This is critical to the business logic)

[1]SO post http://stackoverflow.com/questions/19301798/stripe-card-authentication-passed-from-iphone-failed-on-server