How to set up local authentication using Face ID or Touch ID in an iOS mobile app?

To implement biometric security in your application, the built-in LocalAuthentication framework is used. This tool allows you to securely prompt the user for identity confirmation before performing critical actions, such as transferring funds or viewing confidential data.

The first step is to import the LocalAuthentication module into your source file. Then, an instance of the LAContext class is created, which manages the security policy and interacts with the device hardware for face or fingerprint recognition.

Before calling the authentication method, it is crucial to check the feasibility of using biometrics on the current device. For this, the canEvaluatePolicy method is used by passing the deviceOwnerAuthenticationWithBiometrics parameter, which takes into account the presence of sensors and their state in the system.

If the availability check is successful, the main evaluatePolicy method is called. In it, you pass the selected policy, a localized reason string for the user, and a closure block to handle the result of a successful login or an error that occurred.

It is important to consider that all biometric requests are executed asynchronously and may return specific errors that need to be handled correctly. For example, if the user has locked Face ID or canceled the request manually, the app should offer an alternative login method, such as entering a numeric passcode.