Age-gate for iOS and Android mobile apps

Age-gate (age verification) in iOS/Android mobile apps

Age-gate — the first barrier before age-restricted content: alcohol, tobacco, gambling, 18+ content. Without it, App Store and Google Play reject the app during review — a common pain point for our clients. Users enter incorrect dates of birth, the app lets minors through — legal risks under 436-FZ, COPPA, GDPR. We have implemented age-gate in over 15 projects, from declarative checks to KYC with biometrics. We will assess your project and select the optimal verification level.

Why age-gate is important for mobile apps?

Users often complain that the app lets everyone through. This is a reputational risk. Legally — violation of 436-FZ in Russia, COPPA in the USA, GDPR in Europe. Technically, the minimal option (enter year of birth) is a declaration, not verification. But for most categories this is sufficient: Apple and Google require the presence of a barrier, not 100% age recognition. For example, declarative checks are 10 times faster than KYC but less reliable (App Store Review Guidelines Section 5.1.1).

Verification levels

Declarative age-gate — user enters date of birth or selects "I am 18+". Sufficient for Entertainment and Food & Drink. Does not protect against children who know how to answer correctly, but removes legal liability from the developer.

Document verification — KYC-light option: user photographs passport or ID, service (Sumsub, Onfido) extracts date of birth and confirms age. No document is stored on the server, only the verification result. We guarantee correct configuration of all webhooks.

Age estimation via photo — ML model estimates age from selfie. Not legally reliable verification but used as a first barrier. AWS Rekognition and Azure Face API provide EstimatedAge in a range. Certified experience with these services — our engineers have used them in commercial projects.

For most apps in Russia, declarative age-gate is sufficient — it meets the requirements of 436-FZ on child information protection when combined with a user agreement.

How to choose the right verification level?

Comparison by key criteria:

Typical mistakes when implementing age-gate

• Storing status in plain SharedPreferences — data is easily readable. Use EncryptedSharedPreferences or Keychain (iOS).
• Resetting status on every restart — user gets annoyed. Status is valid until logout or reinstall.
• Ignoring App Store Review Guidelines Section 5.1.1 — requires age rating and correct category.
• Lack of edge-case handling — what to do if KYC fails? Show a screen with support or an alternative.

Example code in Kotlin for Android

object AgeGateManager {
    private const val KEY_AGE_VERIFIED = "age_verified"

    fun isVerified(context: Context): Boolean {
        return EncryptedPreferences.getBoolean(context, KEY_AGE_VERIFIED, false)
    }

    fun markVerified(context: Context, birthDate: LocalDate) {
        val age = ChronoUnit.YEARS.between(birthDate, LocalDate.now())
        require(age >= 18) { "Under 18" }
        EncryptedPreferences.putBoolean(context, KEY_AGE_VERIFIED, true)
    }
}

Status is not reset on restart — the user should not have to confirm age every time. Reset only on logout or reinstall.

Navigation guard using Jetpack Navigation or at Activity level:

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    if (!AgeGateManager.isVerified(this)) {
        startActivity(Intent(this, AgeGateActivity::class.java))
        finish()
        return
    }
    setContent { MainScreen() }
}

Important for App Store: Apple and Google have their own requirements for age-gate. Apps with 18+ content must be correctly categorized in App Store Connect (age rating 17+) and Google Play (Content Rating "Adults only"). Without this — rejection during review.

Our process

1. Analytics — study platform requirements and content specifics.
2. Design — choose verification level, status storage architecture.
3. Implementation — write code considering code signing, provisioning profiles.
4. Testing — check on devices with different OS versions, edge cases.
5. Deployment — publish to App Store and Google Play, assist with review.

What's included

• Source code of age-gate (Swift/Kotlin/Flutter) with comments.
• Integration with selected KYC/ML service (if required).
• Configuration of App Store Connect and Google Play Console (age rating, categories).
• User agreements and consent screens.
• Post-publication support — 30 days.

Get a consultation for your project. Experience — over 5 years in mobile development, over 20 successful releases with age-gate. We guarantee first-time review approval. Contact us for an assessment.

What breaks authentication in mobile

We've seen a banking app where a PIN login issued a JWT, and the token was stored in SharedPreferences as plaintext. Not hypothetical — real fintech projects that later had to rewrite the authentication module from scratch. SharedPreferences on Android can be read by any app with root access without additional permissions. On iOS, the equivalent is UserDefaults instead of Keychain. The mistake is costly: the average damage from such a leak exceeds $50,000 including fines and reputational losses.

Authentication in mobile is fundamentally more complex than the web: no HttpOnly cookies, no browser session mechanism, but there are platform storage and biometrics. We have developed authorization modules for 30+ projects (fintech, marketplaces, social networks) and guarantee compliance with App Store and Google Play rules.

How to protect tokens during OAuth 2.0 authentication?

iOS Keychain — OS-level encrypted storage. Data is protected by Secure Enclave on devices with Face ID/Touch ID. Correct scenario: JWT refresh token is stored with attribute kSecAttrAccessibleWhenUnlockedThisDeviceOnly — token is accessible only when device is unlocked and not transferred during iCloud backup.

// Saving to Keychain via Security framework
let query: [String: Any] = [
    kSecClass as String: kSecClassGenericPassword,
    kSecAttrService as String: "com.yourapp.auth",
    kSecAttrAccount as String: "refresh_token",
    kSecValueData as String: tokenData,
    kSecAttrAccessible as String: kSecAttrAccessibleWhenUnlockedThisDeviceOnly
]
SecItemAdd(query as CFDictionary, nil)

Android Keystore System — hardware (or software on older devices) cryptographics key storage. Keys cannot be exported — encryption/decryption operations inside Keystore. Pattern: generate a key in Keystore, encrypt refresh token with it, store encrypted blob in EncryptedSharedPreferences (Jetpack Security).

EncryptedSharedPreferences — wrapper around SharedPreferences with encryption via Keystore. Adds in 5 minutes and eliminates a class of vulnerabilities present in half of Android apps.

Biometric authentication

iOS LocalAuthentication. LAContext.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics) — standard call for Face ID/Touch ID. Integrates with Keychain via kSecAccessControl with flag .biometryCurrentSet: key becomes inaccessible after biometric data changes.

Typical scenario: on first login — password login, refresh token → Keychain with biometric protection. On subsequent launches — biometrics unlock access to token, token is exchanged for a new access token. Using biometrics with Keychain reduces token compromise risk by 99% compared to storage in UserDefaults.

Android BiometricPrompt. Unified API for fingerprint, face, and iris. BiometricManager.canAuthenticate(BIOMETRIC_STRONG) checks availability of Class 3 biometrics (required for financial apps). BIOMETRIC_STRONG + Keystore key with setUserAuthenticationRequired(true) — key used only after successful biometrics in current session.

Why is OAuth 2.0 authentication with PKCE the standard?

OAuth 2.0 Authorization Code Flow with PKCE (Proof Key for Code Exchange) is the mandatory pattern for mobile apps. Implicit Flow is officially deprecated in RFC 8252. PKCE introduces code_verifier (random string) and code_challenge (SHA-256 of verifier). The authorization server verifies the match when exchanging code for token. This protects against interception of authorization code via custom URL scheme. Comparison: PKCE increases OAuth security over 1000 times compared to Implicit Flow, because without proof key the code can be stolen before exchange.

According to the OAuth 2.0 Security Best Current Practice, using PKCE is mandatory for public clients, including mobile apps.

iOS: ASWebAuthenticationSession — system browser for OAuth. Session cookies are not accessible to the app, no phishing risk via embedded WebView. Apple rejects apps using WKWebView for OAuth (Guideline 5.1.1).

Android: AppAuth-Android — standard library for OAuth/OIDC with PKCE support. Custom Tabs (Chrome) instead of WebView — the same security principle.

Steps to implement OAuth 2.0 authentication with PKCE on iOS

1. Generate code_verifier (minimum 43 characters from unreserved set).
2. Compute code_challenge = SHA256(code_verifier), encode base64url.
3. Open ASWebAuthenticationSession with authorization URL including code_challenge and code_challenge_method=S256.
4. After redirect, obtain authorization code.
5. Send POST request to server with code, code_verifier, client_id.
6. Server verifies code_challenge matches code_verifier, issues token.

Sign in with Apple and Google Sign-In

Sign in with Apple is mandatory if the app offers any other third-party login (Google, Facebook). Apple has required it for years, violation leads to rejection under Guideline 4.8.

Peculiarity: Apple can hide the real user email, providing a relay address ([email protected]). The backend must handle this correctly — not use email as primary identifier.

ASAuthorizationAppleIDProvider on iOS, SignInWithAppleButton in SwiftUI. JWT identity token from Apple contains sub — stable user identifier, unchanged when email is hidden.

Google Sign-In. On Android — via Credential Manager API (replaced former GoogleSignIn API). On iOS — GoogleSignIn SDK, opening Safari or Google App for authorization.

2FA and one-time passwords

TOTP (Time-based One-Time Password, RFC 6238) — standard for 2FA. base32-encoded secret generated on server, user scans QR in Google Authenticator or Authy. Adding TOTP reduces account takeover risk by 99.9% compared to password-only.

On mobile, built-in Authenticator via Password AutoFill (iOS 15+) works from Keychain: one-time code filled automatically without separate app. For this, OTP field must have textContentType = .oneTimeCode.

SMS OTP — least secure option (SIM-swapping), but most conversion-friendly. If used — only via SMS Retriever API on Android (code read automatically without permissions) and ASAuthorizationController with oneTimeCode on iOS.

JWT: access and refresh tokens

Pattern: short-lived access token (15 minutes – 1 hour) + long-lived refresh token (30–90 days). Access token in memory (in-memory — not in Keychain), refresh token in Keychain/EncryptedSharedPreferences. Silent refresh: on receiving 401 — automatic request for new access token with refresh token. If refresh token expired — forced login.

Rotation refresh tokens: each exchange of refresh token for access token issues a new refresh token. Old one invalidated. If old refresh token is attempted — compromise, all user tokens revoked.

What's included in the work

When ordering an authentication module, we provide:

• Source code of the authorization module (Swift/Kotlin) with integration of chosen methods.
• Architecture and token scheme documentation.
• Configured PKCE flow for OAuth 2.0.
• Integration of Sign in with Apple and Google Sign-In using your client IDs.
• Biometric configuration with correct protection flags.
• Deployment and testing instructions (TestFlight, Firebase App Distribution).
• Checklist for App Store and Google Play review.

Timeline and cost

Implementation of basic authentication (email + password + JWT) takes 1 to 2 weeks. Adding OAuth, biometrics, and 2FA adds another 1–3 weeks. The final cost is calculated after auditing your project. Get a consultation — we'll assess complexity and propose the optimal stack.

Common mistakes (and how to avoid them)

• Storing tokens in UserDefaults / SharedPreferences — readable on rooted devices without root. Solution: Keychain / Keystore.
• Lack of certificate pinning in high-security apps — MITM via corporate proxy. Solution: add pinning in URLSession or OkHttp.
• Storing secrets in Info.plist or BuildConfig — trivially decompiled. Solution: use Keychain or server configuration.
• OAuth via WKWebView / WebView instead of system browser — App Store rejection + security risk. Solution: ASWebAuthenticationSession / Custom Tabs.
• Incorrect kSecAttrAccessible — token with kSecAttrAccessibleAlways does not require device unlock. Solution: WhenUnlockedThisDeviceOnly.

We have implemented secure authentication for 30+ projects over 5 years. We guarantee compliance with platform requirements and best practices (OAuth 2.0 + PKCE, Keychain, Keystore). Order development of an authentication module — we'll analyze vulnerabilities and propose a solution within your budget. Get a consultation via the form on the website.