TEAM LICENSES: Save money and learn new skills through a Hacking with Swift+ team license >>

How to use Touch ID to authenticate users by fingerprint

Swift version: 5.10

Paul Hudson    @twostraws   

Touch ID is an easy and secure way for users to authenticate themselves, so its no surprise that it's caught on so quickly among apps. Authenticating with Touch ID automatically uses the fingerprints registered by the user when they set up Touch ID, and you never have access to those fingerprints, which means it's both low-friction and extra-secure.

To get started, you need to import the LocalAuthentication framework like this:

import LocalAuthentication

The actual act of authenticating users has a number of possible results, and you need to catch them all:

  • The user might not have a Touch ID-capable device.
  • The user might have a Touch ID-capable device, but might not have configured it.
  • The user failed to authenticate, perhaps because they asked to enter a passcode rather than use Touch ID.

Note that Apple insists that your app provide a passcode method of authentication as a back up. More annoyingly, you need to request and store this passcode yourself – it's not even done by Apple using the system unlock code!

Asking for and setting a passcode is easy enough, so I'll leave that to you. The important bit is asking for Touch ID authentication, which is done using this code:

func authenticateUser() {
    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 {
                } 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)
Hacking with Swift is sponsored by Superwall.

SPONSORED Superwall lets you build & test paywalls without shipping updates. Run experiments, offer sales, segment users, update locked features and more at the click of button. Best part? It's FREE for up to 250 conversions / mo and the Superwall team builds out 100% custom paywalls – free of charge.

Learn More

Sponsor Hacking with Swift and reach the world's largest Swift community!

Available from iOS 8.0 – see Hacking with Swift tutorial 28

Similar solutions…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

Buy Pro Swift Buy Pro SwiftUI Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let us know!

Average rating: 3.9/5

Unknown user

You are not logged in

Log in or create account

Link copied to your pasteboard.