How to use Touch ID sensor in iOS 8

Question

One of the most things I was excited about iOS 8 was the ability to use fingerprint sensors on the iPhone 5s and later. Unfortunately I cannot find out what is the required framework for that, nor how I can make authentication. Please help me with:

• What framework required for using Touch ID?
• How to use its methods and how to authenticate the user?

A code sample would be much appreciated.

Answer 1

More complete snippet, swift style:

func authenticateUser() {
        // Get the local authentication context.
        let context = LAContext()

        // Declare a NSError variable.
        var error: NSError?

        // Set the reason string that will appear on the authentication alert.
        var reasonString = "Authentication is needed to access your notes."

        // Check if the device can evaluate the policy.
        if context.canEvaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, error: &error) {
            [context .evaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, localizedReason: reasonString, reply: { (success: Bool, evalPolicyError: NSError?) -> Void in

                if success {

                }
                else{
                    // If authentication failed then show a message to the console with a short description.
                    // In case that the error is a user fallback, then show the password alert view.
                    println(evalPolicyError?.localizedDescription)

                    switch evalPolicyError!.code {

                    case LAError.SystemCancel.toRaw():
                        println("Authentication was cancelled by the system")

                    case LAError.UserCancel.toRaw():
                        println("Authentication was cancelled by the user")

                    case LAError.UserFallback.toRaw():
                        println("User selected to enter custom password")
                        self.showPasswordAlert()

                    default:
                        println("Authentication failed")
                        self.showPasswordAlert()
                    }
                }

            })]
        }
        else{
            // If the security policy cannot be evaluated then show a short message depending on the error.
            switch error!.code{

            case LAError.TouchIDNotEnrolled.toRaw():
                println("TouchID is not enrolled")

            case LAError.PasscodeNotSet.toRaw():
                println("A passcode has not been set")

            default:
                // The LAError.TouchIDNotAvailable case.
                println("TouchID not available")
            }

            // Optionally the error description can be displayed on the console.
            println(error?.localizedDescription)

            // Show the custom alert view to allow users to enter the password.
            self.showPasswordAlert()
        }
    }

Source