Implementing Face ID/Touch ID authentication in Swift involves using the Local Authentication framework provided by Apple. Here’s a basic guide to implementing this feature:

1. Import LocalAuthentication Framework: First, import the LocalAuthentication framework in your Swift file where you want to implement Face ID/Touch ID authentication.

import LocalAuthentication

Check Device Support: Before proceeding with authentication, check if the device supports Face ID/Touch ID authentication.

func isBiometricAuthenticationAvailable() -> Bool {
    let context = LAContext()
    var error: NSError?

    return context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error)
}

Authenticate with Face ID/Touch ID: Use the LAContext class to evaluate the biometric authentication policy.

func authenticateWithBiometrics() {
    let context = LAContext()
    var error: NSError?

    if context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error) {
        let reason = "Authenticate to access your account"
        context.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, localizedReason: reason) { success, authenticationError in
            DispatchQueue.main.async {
                if success {
                    // Biometric authentication succeeded
                    // Proceed with your application logic
                } else {
                    // Biometric authentication failed or was canceled by the user
                    if let error = authenticationError {
                        // Handle the error
                    }
                }
            }
        }
    } else {
        // Biometric authentication not available or not configured
        if let error = error {
            // Handle the error
        }
    }
}

1. Handle Authentication Result: In the completion handler of evaluatePolicy, handle the success or failure of biometric authentication. If successful, proceed with your application logic. If authentication fails, handle the error accordingly.
2. Call Authentication Method: Call the authenticateWithBiometrics() method wherever you want to trigger biometric authentication in your app.

authenticateWithBiometrics()

Optional: Customize Authentication UI: You can customize the biometric authentication prompt by setting a custom localized reason and fallback button title.

let context = LAContext()
context.localizedFallbackTitle = "Enter Passcode"

By following these steps, you can implement Face ID/Touch ID authentication in your Swift app using the Local Authentication framework. Make sure to handle errors and provide appropriate feedback to users during the authentication process.