Biometric authentication in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the package needed for biometric authentication in Flutter.

Flutter

import '[1]';

Drag options to blanks, or click blank then click option'

Acupertino_icons/cupertino_icons.dart

Bflutter/material.dart

Cdart:async

Dlocal_auth/local_auth.dart

Attempts:

3 left

💡 Hint

Common Mistakes

Importing unrelated packages like material.dart or cupertino_icons.

Forgetting to import the biometric package.

The 'local_auth/local_auth.dart' package provides biometric authentication features in Flutter.

2fill in blank

medium

Complete the code to create an instance of the LocalAuthentication class.

Flutter

final LocalAuthentication auth = [1]();

Drag options to blanks, or click blank then click option'

ABiometricAuth

BLocalAuthentication

CAuthLocal

DAuthenticationLocal

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect class names like BiometricAuth.

Confusing the class name with variable names.

The LocalAuthentication class is used to access biometric authentication methods.

3fill in blank

hard

Fix the error in the code to check if biometric authentication is available.

Flutter

bool canCheck = await auth.[1]();

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AcanCheckBiometrics

BisDeviceSupported

Cauthenticate

DcheckBiometrics

Attempts:

3 left

💡 Hint

Common Mistakes

Using authenticate() which starts the authentication process instead of checking availability.

Using isDeviceSupported() which checks device support but not biometric enrollment.

The method canCheckBiometrics() returns true if biometric hardware is available and enrolled.

4fill in blank

hard

Fill both blanks to start biometric authentication with a localized reason and options.

Flutter

bool authenticated = await auth.[1](
  localizedReason: '[2]',
  options: const AuthenticationOptions(
    stickyAuth: true,
  ),
);

Drag options to blanks, or click blank then click option'

Aauthenticate

BauthenticateWithBiometrics

CstartAuthentication

DPlease authenticate to proceed

Attempts:

3 left

💡 Hint

Common Mistakes

Using deprecated or incorrect method names.

Not providing a clear localizedReason string.

The authenticate() method starts the biometric prompt with a reason shown to the user.

5fill in blank

hard

Fill all three blanks to handle authentication failure and success with messages.

Flutter

try {
  bool success = await auth.[1](
    localizedReason: '[2]',
  );
  if (success) {
    print('[3]');
  } else {
    print('Authentication failed');
  }
} catch (e) {
  print('Error: $e');
}

Drag options to blanks, or click blank then click option'

Aauthenticate

BPlease verify your identity

CAuthentication successful

DauthenticateWithBiometrics

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong method names.

Not handling exceptions properly.

The authenticate() method is called with a reason, and success or failure messages are printed accordingly.

Practice

1. What is the main purpose of biometric authentication in a Flutter app?

easy

A. To send notifications to users

B. To change the app's theme colors automatically

C. To speed up app loading times

D. To secure the app using fingerprint or face recognition

Solution

1. Step 1: Understand biometric authentication

   Biometric authentication uses unique physical traits like fingerprint or face to secure access.

2. Step 2: Identify its purpose in apps

   It protects sensitive data by allowing only authorized users to enter.

3. Final Answer:

   To secure the app using fingerprint or face recognition -> Option D

4. Quick Check:

   Biometric authentication = Secure app access [OK]

Hint: Biometrics means using your body to unlock [OK]

Common Mistakes:

• Confusing biometric authentication with UI changes
• Thinking it improves app speed
• Assuming it sends notifications

2. Which Flutter package is commonly used to implement biometric authentication?

easy

A. local_auth

B. shared_preferences

C. provider

D. http

Solution

1. Step 1: Recall Flutter packages for biometrics

   The local_auth package provides access to fingerprint and face authentication.

2. Step 2: Compare with other packages

   http is for network calls, provider for state management, and shared_preferences for storing data.

3. Final Answer:

   local_auth -> Option A

4. Quick Check:

   Biometric package = local_auth [OK]

Hint: local_auth sounds like local device authentication [OK]

Common Mistakes:

• Choosing http for biometrics
• Confusing provider with authentication
• Picking shared_preferences for biometrics

3. What will the following Flutter code print if biometric authentication is available and successful?

final isAvailable = await auth.canCheckBiometrics;
if (isAvailable) {
  final didAuthenticate = await auth.authenticate(
    localizedReason: 'Please authenticate',
  );
  print(didAuthenticate);
} else {
  print('No biometrics');
}

medium

A. No biometrics

B. false

C. true

D. Exception error

Solution

1. Step 1: Check biometric availability

   The code checks if biometrics are available with canCheckBiometrics. If true, it proceeds.

2. Step 2: Authenticate and print result

   If authentication succeeds, didAuthenticate is true and printed.

3. Final Answer:

   true -> Option C

4. Quick Check:

   Available and success = true [OK]

Hint: Success prints true, failure prints false or message [OK]

Common Mistakes:

• Assuming it prints 'No biometrics' when available
• Expecting false on success
• Ignoring await causing errors

4. Identify the error in this Flutter biometric authentication snippet:

final didAuthenticate = await auth.authenticate(
  localizedReason: 'Scan fingerprint',
  useErrorDialogs: true,
  stickyAuth: true
);
if (didAuthenticate) {
  print('Access granted');
}

medium

A. No check if biometrics are available before authenticate

B. Incorrect parameter name localizedReason

C. Missing await keyword before authenticate

D. Missing else block after if

Solution

1. Step 1: Review biometric availability check

   The code calls authenticate without checking canCheckBiometrics first, which may cause errors on devices without biometrics.

2. Step 2: Validate other parts

   Await is present, parameter names are correct, and else block is optional.

3. Final Answer:

   No check if biometrics are available before authenticate -> Option A

4. Quick Check:

   Always check availability before authenticate [OK]

Hint: Check biometrics availability before authenticating [OK]

Common Mistakes:

• Skipping availability check
• Confusing parameter names
• Thinking else block is mandatory

5. You want to secure a Flutter app so it only allows access if biometric authentication succeeds. Which sequence of steps correctly implements this using local_auth? A) Call authenticate directly without checking availability. B) Check canCheckBiometrics, then call authenticate, then proceed if true. C) Skip biometric checks and use a password instead. D) Call authenticate and ignore its result.

hard

A. Call authenticate directly without checking availability

B. Check canCheckBiometrics, then authenticate, then proceed if true

C. Skip biometrics and use password only

D. Call authenticate and ignore its result

Solution

1. Step 1: Verify biometric availability

   Use canCheckBiometrics to ensure device supports biometrics before authenticating.

2. Step 2: Authenticate and check result

   Call authenticate and proceed only if it returns true, ensuring secure access.

3. Step 3: Avoid skipping checks or ignoring results

   Skipping availability or ignoring authentication result risks security.

4. Final Answer:

   Check canCheckBiometrics, then authenticate, then proceed if true -> Option B

5. Quick Check:

   Availability check + authenticate success = secure access [OK]

Hint: Always check availability before authenticating [OK]

Common Mistakes:

• Calling authenticate without availability check
• Ignoring authentication result
• Using password instead of biometrics when asked