How to use Touch ID sensor in iOS 8 - ios

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

Answer 2

The Local Authentication framework provides facilities for requesting authentication from users using Touch ID, following code snipped shows how you should request for authentication.
Objective C
LAContext *myContext = [[LAContext alloc] init];
NSError *authError = nil;
NSString *myReasonString = #"String explaining why app needs authentication";
if ([myContext canEvaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics error:&authError]) {
[myContext evaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics
localizedReason:myReasonString
reply:^(BOOL succes, NSError *error) {
if (success) {
// User authenticated successfully
} else {
// Authenticate failed
}
}];
} else {
// Could not evaluate policy; check authError
}
Swift
let myContext = LAContext()
var authError: NSError?
// Set the reason string that will appear on the authentication alert.
var myReasonString = "String explaining why app needs authentication"
if myContext.canEvaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, error: &authError) {
[myContext.evaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, localizedReason: myReasonString, reply: { (success: Bool, evalPolicyError: NSError?) -> Void in
if success {
// User authenticated successfully
} else {
// Authenticate failed
}
})]
} else{
// Could not evaluate policy; check authError
}

Answer 3

You're looking for LocalAuthentication framework (login may be required to see).
Basically you're interested in LAContext class and its
canEvaluatePolicy:error: and
evaluatePolicy:localizedReason:reply: methods.
The canEvaluatePolicy:error: method is used to check if TouchID authentication is available for you to use.
And use evaluatePolicy:localizedReason:reply: to perform actual authentication check

Answer 4

I was looking for an answer in objectiveC with all the possible errors. Didn't find on this post so here it is.
LAContext *myContext = [[LAContext alloc] init];
NSError *authError = nil;
NSString *myLocalizedReasonString = #"Authenticate using your finger";
if ([myContext canEvaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics error:&authError]) {
[myContext evaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics
localizedReason:myLocalizedReasonString
reply:^(BOOL success, NSError *error) {
if (success) {
NSLog(#"User is authenticated successfully");
} else {
switch (error.code) {
case LAErrorAuthenticationFailed:
NSLog(#"Authentication Failed");
break;
case LAErrorUserCancel:
NSLog(#"User pressed Cancel button");
break;
case LAErrorUserFallback:
NSLog(#"User pressed Enter Password");
break;
case LAErrorPasscodeNotSet:
NSLog(#"Passcode Not Set");
break;
case LAErrorTouchIDNotAvailable:
NSLog(#"Touch ID not available");
break;
case LAErrorTouchIDNotEnrolled:
NSLog(#"Touch ID not Enrolled or configured");
break;
default:
NSLog(#"Touch ID is not configured");
break;
}
NSLog(#"Authentication Fails");
}
}];
} else {
NSLog(#"Can not evaluate Touch ID. This device doesn’t support one");
}
Also make sure to use dispatch_async otherwise your uialert messages will not pop-up on time. See sample code below
-(void)viewWillAppear:(BOOL)animated {
LAContext *myContext = [[LAContext alloc] init];
NSError *authError = nil;
NSString *myLocalizedReasonString = #"Touch ID Test to show Touch ID working in a custom app";
if ([myContext canEvaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics error:&authError]) {
[myContext evaluatePolicy:LAPolicyDeviceOwnerAuthenticationWithBiometrics
localizedReason:myLocalizedReasonString
reply:^(BOOL success, NSError *error) {
if (success) {
dispatch_async(dispatch_get_main_queue(), ^{
[self performSegueWithIdentifier:#"Success" sender:nil];
});
} else {
dispatch_async(dispatch_get_main_queue(), ^{
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:#"Error"
message:error.description
delegate:self
cancelButtonTitle:#"OK"
otherButtonTitles:nil, nil];
[alertView show];
// Rather than show a UIAlert here, use the error to determine if you should push to a keypad for PIN entry.
});
}
}];
} else {
dispatch_async(dispatch_get_main_queue(), ^{
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:#"Error"
message:authError.description
delegate:self
cancelButtonTitle:#"OK"
otherButtonTitles:nil, nil];
[alertView show];
// Rather than show a UIAlert here, use the error to determine if you should push to a keypad for PIN entry.
});
}
}

Answer 5

Swift 3 version of #txulu response:
public 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 {
// TODO - Guardar credencials
}
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.
print(evalPolicyError?.localizedDescription)
switch evalPolicyError!.code {
case LAError.systemCancel.rawValue:
print("Authentication was cancelled by the system")
case LAError.userCancel.rawValue:
print("Authentication was cancelled by the user")
case LAError.userFallback.rawValue:
print("User selected to enter custom password")
//self.showPasswordAlert()
default:
print("Authentication failed")
//self.showPasswordAlert()
}
}
} as! (Bool, Error?) -> Void)]
}
else{
// If the security policy cannot be evaluated then show a short message depending on the error.
switch error!.code{
case LAError.touchIDNotEnrolled.rawValue:
print("TouchID is not enrolled")
case LAError.passcodeNotSet.rawValue:
print("A passcode has not been set")
default:
// The LAError.TouchIDNotAvailable case.
print("TouchID not available")
}
// Optionally the error description can be displayed on the console.
print(error?.localizedDescription)
// Show the custom alert view to allow users to enter the password.
//self.showPasswordAlert()
}
}

Answer 6

Full Swift 5 version example snippet:
import LocalAuthentication
_
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.
let reasonString = "Authentication is needed to provide access."
// 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: Error?) -> Void in
if success {
print("Authentication successful! :) ")
} 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.
print(evalPolicyError?.localizedDescription)
switch evalPolicyError!._code {
case LAError.authenticationFailed.rawValue:
print("### Authentication was cancelled by the system")
case LAError.userCancel.rawValue:
print("### Authentication was cancelled by the user")
case LAError.userFallback.rawValue:
print("### User selected to enter custom password")
self.showPasswordAlert()
default:
print("### 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.biometryNotEnrolled.rawValue:
print("### TouchID is not enrolled")
case LAError.passcodeNotSet.rawValue:
print("### A passcode has not been set")
default:
// The LAError.TouchIDNotAvailable case.
print("### TouchID not available")
}
// Optionally the error description can be displayed on the console.
print(error?.localizedDescription)
// Show the custom alert view to allow users to enter the password.
self.showPasswordAlert()
}
}
func showPasswordAlert() {
print("### showPasswordAlert")
}

Answer 7

Among these answers I was getting stuck every time I was running the authentication code.
Please make sure you Import LocalAuthentication to use LAContext and privacy check
With Swift 5 this is what worked for me.
import UIKit
import LocalAuthentication
class ViewController: UIViewController {
#IBOutlet weak var lbl: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func checkUserAuthentication(_ sender: Any) {
let context = LAContext()
var error: NSError?
if context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error) {
let reason = "Identify yourself!"
context.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: reason) {
[unowned self] success, authenticationError in
DispatchQueue.main.async {
if success {
//Authentication Success
self.lbl.text = "Great!! you are authorised"
} else {
let ac = UIAlertController(title: "Authentication failed", message: "Sorry!", preferredStyle: .alert)
ac.addAction(UIAlertAction(title: "OK", style: .default))
self.present(ac, animated: true)
}
}
}
} else {
let ac = UIAlertController(title: "Touch ID not available", message: "Your device is not configured for Touch ID.", preferredStyle: .alert)
ac.addAction(UIAlertAction(title: "OK", style: .default))
present(ac, animated: true)
}
}
}