Mobile App Authentication

TL;DR

Secure your mobile app with strong authentication methods like multi-factor authentication (MFA), biometric login, and robust session management. Prioritise user experience while protecting against common threats.

1. Choose Your Authentication Methods

Several options exist; pick what suits your app’s security needs and target audience:

• Password-based: The most basic, but weakest. Enforce strong password policies (length, complexity).
• Multi-Factor Authentication (MFA): Adds an extra layer of security – something the user knows (password) and something they have (code from SMS, authenticator app). Highly recommended.
• Biometric Login: Uses fingerprints or facial recognition. Convenient but relies on device capabilities.
• Social Login: Allows users to log in with existing accounts (Google, Facebook). Simplifies registration but introduces third-party dependencies.

2. Implement MFA

MFA significantly improves security. Here’s a basic outline:

1. Registration: When the user signs up, collect their phone number or email address for verification.
2. Verification Code Generation: Generate a random code (e.g., 6-digit) and send it via SMS or email.
3. Code Validation: Ask the user to enter the code during login. Verify against the generated code.

Example using Python:

import random

def generate_code():
    return str(random.randint(100000, 999999))

# In a real app, you'd use an SMS gateway or email service.
verification_code = generate_code()
print(f"Verification code: {verification_code}")

3. Secure Biometric Authentication

Use the device’s built-in biometric APIs (Touch ID, Face ID) instead of implementing your own.

• Android: Use the BiometricPrompt API.
• iOS: Use the LocalAuthentication framework.

Always handle errors gracefully (e.g., user cancels, biometric sensor unavailable).

4. Robust Session Management

Manage user sessions securely to prevent unauthorized access:

• Unique Session IDs: Generate strong, random session IDs for each login.
• Session Expiration: Set a reasonable expiration time for sessions (e.g., 30 minutes of inactivity).
• Secure Storage: Store session IDs securely (encrypted) on the server and client-side.
• Invalidate Sessions on Logout: Clear the session ID when the user logs out.

5. Protect Against Common Threats

• Brute-Force Attacks: Implement rate limiting to prevent excessive login attempts.
• Session Hijacking: Use HTTPS and secure cookies (HttpOnly, Secure flags).
• Man-in-the-Middle (MITM) Attacks: Enforce HTTPS for all communication.
• Credential Stuffing: Monitor for compromised credentials and alert users if their accounts are affected.

6. Data Security Best Practices

• Never store passwords in plain text. Use strong hashing algorithms (e.g., bcrypt, Argon2).
• Encrypt sensitive data both in transit and at rest.
• Regularly update your dependencies to patch security vulnerabilities.