Implementing the authentication logic

- [Instructor] Next, let's implement…the authentication logic.…The local authentication API is simple and straightforward.…I call the authentication context, Evaluate Policy Method.…It's an asynchronous method and it involves…prompting the user for authentication.…We need to provide the policy to evaluate,…which again is LAPolicy…deviceOwnerAuthenticationWithBiometrics.…The localized reason parameter should be…a localized message.…

Let's say Log in with your Touch ID.…The system displays this message in the…authentication dialog presented to the user.…The third parameter is the reply closure…that's executed when the evaluation finishes.…The closure has a Boolean parameter…that indicates whether the policy evaluation succeeded…and an optional error, which is nil…if there were no problems.…Let's call it success…and error.…

For this demo, I'm going to pop up an alert view…showing if the authentication was successful or not.…So, I create two string variables…for the title and the message.…var title…and let's initialize it with Success.…