How to Handle App Permissions Securely: Best Practices for Protecting User Trust and Data

📘 Chapter 4: Secure Storage and Usage of Granted Permissions

🔍 Overview

Gaining access to user data through permissions is only half the challenge—what you do with that data defines the trustworthiness, security, and compliance of your app. Once permission is granted, developers are responsible for safely storing, accessing, and updating sensitive information.

This chapter will explore:

• The principles of secure permission-related data usage
• How to store user data responsibly (locally and remotely)
• Platform APIs for safe storage
• Preventing misuse, leaks, and unintended exposure
• Securely handling revocations and resets
• Best practices and code examples for both Android and iOS

🔐 1. Core Principles of Secure Data Usage

Before you store or use permission-protected data, ensure you follow these principles:

✅ Least Privilege

Access only what is absolutely necessary, and only when needed.

✅ Secure by Design

Encrypt, anonymize, and validate all incoming data.

✅ Real-Time Validation

Never assume continued access—check permission status before each use.

✅ Local First, Cloud Carefully

Prefer local storage unless remote sync is essential. Encrypt both.

✅ Transparency and Control

Let users see, delete, or revoke data associated with their permissions.

📦 2. Where to Store Sensitive Data

🔒 iOS Secure Storage Options

1. Keychain – Secure for storing credentials or session tokens
2. App Sandbox – Store files only accessible by your app
3. UserDefaults – For non-sensitive small flags/settings
4. FileManager – For larger documents and media, stored inside app container

🔒 Android Secure Storage Options

1. EncryptedSharedPreferences – Secure key-value pair storage
2. Android Keystore – Secure cryptographic key storage
3. Room (Encrypted SQLite) – Persistent, structured data
4. Internal Storage – Private app directory
5. External Storage – Only for user-visible files (use with care)

✅ iOS Keychain Usage Example (Swift)

swift

let query: [String: Any] = [

    kSecClass as String: kSecClassGenericPassword,

    kSecAttrAccount as String: "user_token",

    kSecValueData as String: token.data(using: .utf8)!

]

SecItemAdd(query as CFDictionary, nil)

✅ Android EncryptedSharedPreferences (Kotlin)

kotlin

val masterKey = MasterKey.Builder(context)

    .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)

    .build()

val securePrefs = EncryptedSharedPreferences.create(

    context,

    "secure_prefs",

    masterKey,

    EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,

    EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM

)

securePrefs.edit().putString("token", "abcd1234").apply()

🚨 3. Data Validation & Sanitization

Whenever permission-based data enters your app, treat it as untrusted input:

• Validate formats (e.g., email, phone, GPS coordinates)
• Sanitize metadata (e.g., camera image EXIF data)
• Limit data scope (e.g., crop images to remove sensitive edges)
• Avoid persistent identifiers unless essential

🔁 4. Real-Time Permission Checks Before Access

Never assume that permissions remain granted forever. On both platforms, permissions can be revoked in system settings.

✅ iOS Example

swift

let status = PHPhotoLibrary.authorizationStatus()

if status == .authorized {

    // Proceed with access

} else {

    // Show access request or fallback

}

✅ Android Example

kotlin

if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)

    == PackageManager.PERMISSION_GRANTED) {

    // Access GPS

}

❌ 5. What NOT to Do After Gaining Permission

🧹 6. Handling Revocations and Permission Resets

If a user revokes permission:

• Clear or obfuscate stored data
• Disable related features gracefully
• Offer option to reconnect permission

Example: Handling Revoked Camera Access (iOS)

swift

if AVCaptureDevice.authorizationStatus(for: .video) == .denied {

    // Show fallback or alert

}

Example: Handling Android Revocations

kotlin

override fun onResume() {

    if (!hasPermission()) {

        // Clear cached data or restrict feature

    }

}

🧩 7. Logging, Auditing & User Visibility

For sensitive apps (e.g., finance, healthcare):

• Maintain logs of when data was accessed
• Provide user-facing dashboards of what permissions are granted
• Allow easy revocation or deletion of associated data

Example:

“You shared your location with this app on April 20, 2025. You can remove it from Settings.”

📋 8. Common Permission Storage Workflows

🧠 9. Encryption and Tokenization Strategies

• Use AES-256 or ChaCha20 encryption
• Store encryption keys in the Keychain (iOS) or Keystore (Android)
• Use JWTs or OAuth2 tokens instead of passwords
• Anonymize user identifiers when syncing to cloud

🧪 10. Secure Testing Guidelines

• Test storage using physical device and emulator
• Use intercept tools (like Charles Proxy) to verify secure API handling
• Simulate permission revocation and confirm graceful fallback
• Ensure no unencrypted logs or data leaks in crash reports
• Check compliance with OWASP Mobile Top 10

📌 Conclusion

Handling permissions doesn’t end at the dialog box—it extends into how you store, manage, and clean up the data they unlock. Follow the principles of least privilege, minimal retention, and transparent use to build apps that respect user data, avoid compliance issues, and perform securely under scrutiny.

In the next chapter, we’ll explore tools and frameworks that simplify secure permission handling across platforms.