iOS Touch ID Identity Authentication

iOS Touch ID Identity Authentication

Devices that have fingerprints recorded in iOS 8 and later can use touch ID to authenticate their identity. Only when fingerprints meet the entered fingerprint can the authentication be successful.

step

1. Import LocalAuthentication framework: import LocalAuthentication
2. Initialize the LAContext object: let context = LAContext()
3. Calling the LAContext object canEvaluatePolicy(_ policy: LAPolicy, error: NSErrorPointer) -> Bool method
4. If false is returned in the previous step, it means that authentication cannot be performed and the corresponding failed operation is performed; if true is returned, call the evaluatePolicy(_ policy: LAPolicy, localizedReason: String, reply: @escaping (Bool, Error?) -> Void) method of the LAContext object to determine whether the authentication is successful and the corresponding operation is performed (if the authentication fails, you can get the error code code and see which type of error belongs to to perform the corresponding failed operation)

The canEvaluatePolicy and evaluatePolicy methods that call the LAContext object must both pass in the value of the LAPolicy enumeration type. Currently, there are two values: deviceOwnerAuthenticationWithBiometrics and deviceOwnerAuthentication.The former deviceOwnerAuthenticationWithBiometrics is to perform fingerprint authentication. The latter deviceOwnerAuthentication can only be used in iOS 9.0 and later. Fingerprint authentication is first performed. If fingerprint authentication fails, you can authenticate by entering your password.

Calling the evaluatePolicy method of the LAContext object will pop up the fingerprint authentication dialog box.The dialog box will display the reason why authentication is required, which is the value of the localizedReason parameter. The dialog box has a Cancel button. In iOS 10.0 and later, you can set the localizedCancelTitle value of the LAContext object to change the words displayed by the Cancel button. If fingerprint authentication fails, the dialog box will also display the fallback button. You can set the value of localizedFallbackTitle of the LAContext object to change the words displayed by the fallback button.

It should be noted that the reply callback of the evaluatePolicy method is not in the main thread. If you need to update the UI, you need to call the main thread and update it.

Code Example

The code has been uploaded to GitHub:/Silence-GitHub/TouchIDDemo

Place a label in the controller to display the authentication return result.

Fingerprint authentication code

let context = LAContext()
 = "Fall back button"
if #available(iOS 10.0, *) {
  = "Cancel button"
}
var authError: NSError?
if (.deviceOwnerAuthenticationWithBiometrics, error: &authError) {
 (.deviceOwnerAuthenticationWithBiometrics, localizedReason: "Localized reason for authentication with biometrics", reply: { (success, evaluateError) in
 // NOT in main thread
  {
 if success {
  = "Success"
 // Do something success
 } else if let error = evaluateError {
  = 
 // Deal with error
 if let code = (rawValue: (error as NSError).code) {
  switch code {
  case .userFallback:
  print("fall back button clicked")
  default:
  break
  }
 }
 }
 } 
 })
} else if let error = authError {
  = 
 // Deal with error
}

Fingerprint and password authentication code

if #available(iOS 9.0, *) {
 let context = LAContext()
  = "Fall back button"
 if #available(iOS 10.0, *) {
  = "Cancel button"
 }
 var authError: NSError?
 if (.deviceOwnerAuthentication, error: &authError) {
 (.deviceOwnerAuthentication, localizedReason: "Localized reason for authentication", reply: { (success, evaluateError) in
 // NOT in main thread
  {
 if success {
   = "Success"
  // Do something success
 } else if let error = evaluateError {
   = 
  // When fall back button clicked, user is required to enter PIN. Error code will not be "userFallback"
  // Deal with error
 }
 }
 })
 } else if let error = authError {
  =  
 // Deal with error
 }
} else {
 let alert = UIAlertController(title: nil, message: "Authentication is available on iOS 9.0 or later", preferredStyle: .alert)
 (UIAlertAction(title: "OK", style: .default, handler: nil))
 present(alert, animated: true, completion: nil)
}

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