TL;DR
Use a standard authentication flow (like OAuth 2.0 or OpenID Connect) with strong passwords, multi-factor authentication, and secure token storage to protect your website and mobile app logins.
1. Choose an Authentication Method
Don’t build your own authentication system from scratch! It’s very hard to get right and keep secure. Use a well-established standard:
- OAuth 2.0: Great for letting users log in with Google, Facebook, etc.
- OpenID Connect (OIDC): Builds on OAuth 2.0 and adds user identity information. Good for single sign-on across multiple apps.
- JSON Web Tokens (JWT): A standard way to securely transmit information between parties as a JSON object. Often used with OIDC.
For simplicity, we’ll focus on OAuth 2.0/OIDC using a provider like Auth0 or Firebase Authentication.
2. Website Authentication
- Register your website with the authentication provider: This gives you a Client ID and Client Secret. Keep this secret safe!
- Implement the OAuth 2.0/OIDC flow:
- Redirect users to the provider’s login page.
- After successful login, the provider redirects back to your website with an authorization code.
- Exchange the authorization code for access and refresh tokens using your Client ID and Secret (server-side!).
- Use the access token to access user information from the provider’s API.
- Secure Token Storage: Store refresh tokens securely in a database, encrypted at rest. Never store sensitive credentials directly in client-side code (JavaScript). Use HTTPOnly cookies for session management where appropriate.
Example (simplified) JavaScript redirect:
window.location = "https://your-auth-provider.com/authorize?client_id=YOUR_CLIENT_ID&redirect_uri=YOUR_REDIRECT_URI&response_type=code";3. Mobile App Authentication
- Register your app with the authentication provider: Similar to the website, get a Client ID and Secret.
- Implement the OAuth 2.0/OIDC flow (using a suitable SDK): Most providers offer mobile SDKs for iOS and Android.
- The SDK handles the complexities of token exchange and refresh.
- Use PKCE (Proof Key for Code Exchange) to enhance security, especially in native apps.
- Secure Token Storage: Use secure storage mechanisms provided by the mobile operating system.
- iOS: Keychain
- Android: Keystore System
Example (conceptual) Android code snippet using a Firebase Authentication SDK:
FirebaseAuth.getInstance().signInWithCredential(AuthCredential credential);4. Strong Password Policies
- Minimum length: 12 characters or more
- Complexity requirements: Include uppercase letters, lowercase letters, numbers, and symbols.
- Password hashing: Use a strong hashing algorithm like bcrypt or Argon2 to store passwords securely in the database (server-side). Never store passwords in plain text!
- Regular password updates: Encourage users to change their passwords periodically.
5. Multi-Factor Authentication (MFA)
Add an extra layer of security by requiring a second form of verification, such as:
- One-Time Passwords (OTP): Sent via SMS or email
- Authenticator Apps: Google Authenticator, Authy
- Biometrics: Fingerprint scanning, facial recognition
MFA significantly reduces the risk of account compromise.
6. Security Best Practices
- HTTPS: Always use HTTPS to encrypt communication between your website/app and the server.
- Input Validation: Validate all user input on both client-side and server-side to prevent injection attacks.
- Regular Security Audits: Conduct regular security audits and penetration testing to identify vulnerabilities.
- Keep Libraries Updated: Regularly update your authentication libraries and dependencies to patch security flaws.