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The video says that we should call signOn() as soon as possible even before the user focuses the username text field (e.g. in viewDidLoad). This method is supposed to obtain a challenge from the server and create authorization provider, request & controller and eventually call: controller.performAutoFillAssistedRequests(). But that means that the challenge from the server is needed before the username is known so... How can the server know which public key should it use to construct the challenge?