Mobile App Security Best Practices: Protecting Your Users and Data

Layer 1: The Database (Row Level Security)

The days of relying solely on API logic to protect your data are over. Modern security starts at the database engine.

Row Level Security (RLS)

PostgreSQL offers a superpower called RLS. It essentially says: "No matter HOW you ask for the data—via API, console, or bug—if you aren't the owner, you can't see it."

The Old Way (Vulnerable):

// API Layer
app.get('/notes', (req, res) => {
  // If developer forgets to add "WHERE user_id = req.user.id" here...
  // ...every user sees EVERYONE'S notes. Data leak.
  const notes = db.query('SELECT * FROM notes');
});

The StartAppLab Way (Secure via RLS): We define a policy directly on the Postgres table:

CREATE POLICY "Users can only see their own notes"
ON notes
FOR SELECT
USING (auth.uid() = user_id);

Now, even SELECT * FROM notes returns typically only the rows belonging to that user. The database itself enforces the privacy boundaries. This prevents 90% of accidental data leaks caused by developer error.

Layer 2: Authentication & Token Storage

How does the app prove who it is?

JWTs vs. Sessions

Mobile apps favor JSON Web Tokens (JWT) because they are stateless. The server doesn't need to look up a session in Redis for every API call; it just validates the cryptographic signature of the token.

The Storage Dilemma: Where to put the Token?

This is the most common vulnerability in mobile apps including React Native.

• Bad: Storing tokens in AsyncStorage or SharedPreferences (plain text storage). If a malicious app gains root access or you have an XSS vulnerability in a web view, these tokens can be stolen.
• Good: Using the OS-level secure enclaves.
  • iOS: Keychain Services.
  • Android: EncryptedSharedPreferences (Keystore).

Builder's Tip: In StartAppLab, our auth client automatically wraps these native secure storage mechanisms. You just call auth.login(), and we handle the encryption. You don't need to write native modules to securely store a Refresh Token.

Layer 3: API Communication

HTTPS / TLS is not optional

You must force HTTPS. But for mobile, you should go further with Certificate Pinning. Pinning ensures your app only talks to your server's specific certificate. This prevents "Man-in-the-Middle" (MITM) attacks where a hacker on a public Wi-Fi network intercepts requests by pretending to be your API.

Input Validation (Zod)

Never trust the client. A hacker can bypass your beautiful UI and send curl requests directly to your API endpoint. If your API expects { age: 25 } but receives { age: "select * from users" }, you have a SQL injection problem (if not using an ORM).

We recommend using Zod for strict schema validation on both the frontend and backend.

// Shared Zod Schema
const UserUpdateSchema = z.object({
  username: z.string().min(3).max(20),
  bio: z.string().max(160),
  // Specifically disallow sensitive fields like 'role' or 'is_admin'
});

By sharing this schema, you get Type safety in React Native and Runtime safety in your Node/Next.js backend.

Layer 4: Client-Side Obfuscation

You strictly cannot hide secrets in your mobile app code. Strings like AWS_SECRET_KEY or STRIPE_SECRET_KEY inside your React Native JavaScript bundle are public. Anyone can unzip your .ipa or .apk file and grep for "SECRET".

Rule:

• Public Keys: Safe to be in the app (e.g., Firebase Config, Stripe Public Key).
• Secret Keys: NEVER in the app. If you need to perform a privileged action (like creating a payment intent), the app must ask your Server to do it, and the Server uses the secret key.

Proguard and Hermes

While you can't hide secrets, you should make it hard to reverse-engineer your logic.

• Android: Enable R8/Proguard to minify and obfuscate Java/Kotlin code.
• React Native: Enabling the Hermes engine compiles your JS into bytecode. This makes it significantly harder (though not impossible) for someone to read your source code compared to a plain JS bundle.

Layer 5: Supply Chain Security

Modern apps are built on thousands of npm packages. "Is React Native Secure?" matters less than "Is that random date-picker library I installed secure?"

1. Lock your dependencies: Commit your package-lock.json or yarn.lock.
2. Audit: Run npm audit in your CI/CD pipeline.
3. Minimalism: Don't install a heavy library for a simple function. Every dependency is a potential entry point for a malicious actor.

Conclusion

Security is a game of depth. There is no silver bullet. By implementing RLS at the bottom, Standardize Auth Standards in the middle, and Secure Storage at the top, you create a defense-in-depth strategy that makes your app a hard target.

At StartAppLab, we treat security as a default, not a feature. Our templates come with configured RLS policies, secure storage adapters, and Zod validation pipelines out of the box—so you don't have to become a security researcher just to launch an MVP.