Secure Your Android App with Biometric SDK in 5 Minutes 🔐 (Kotlin)

#android #kotlin #security #opensource

🔐 Biometric SDK for Android

A production-grade biometric authentication SDK designed for apps that demand trust.

Ideal for fintech, banking, e-wallets, secure messaging, parental control, or any app requiring identity protection and transaction-level security.

This SDK simplifies AndroidX biometric integration with modern Kotlin practices, supporting:

Fingerprint
Face Unlock
Device Credential fallback (PIN/Pattern/Password)

Built for real-world apps where authentication reliability is non-negotiable.

🚀 Key Features

✅ Seamless integration with AndroidX Biometric APIs
✅ Supports Fingerprint, Face, and Device Credential fallback
✅ Designed for fintech, banking, and high-trust apps
✅ NOT_ENABLED, ENABLED_AND_MANDATORY, ENABLED_BUT_NOT_MANDATORY auth modes
✅ Lifecycle-safe: no biometric prompts while app is backgrounded
✅ Clean Kotlin interfaces — easy to test with MockK
✅ Pluggable, SDK-ready structure — ideal for JitPack/Maven distribution

📦 Installation via JitPack

Use this SDK directly in your Android project using JitPack.

✅ Step 1: Add JitPack to repositories

In your root-level settings.gradle.kts:

dependencyResolutionManagement {
    repositories {
        maven { url = uri("https://jitpack.io") }
    }
}

✅ Step 2: Add the SDK dependency

In your module-level build.gradle.kts:

implementation("com.github.NoNCoderF:biometric-sdk:v1.0.3")

🧑‍💻 Usage Guide

This SDK offers two flexible integration modes depending on your product's security needs:

🔐 Mode 1: Identity Protection Mode (On-Demand Authentication)

Best for apps that want to secure specific features like viewing a profile, accessing settings, or opening sensitive notes.

Biometric is triggered manually when the user takes a high-trust action.

✅ Example: Trigger Auth Before Showing Profile

private val biometricAuthenticator: BiometricAuthenticator by lazy {
    val biometricManager = MyBiometricManagerImpl(
        this,
        "Unlock",
        "Unlock to use the app"
    )

    BiometricAuthenticatorImpl(
        biometricManager,
        this
    )
}

private val biometricAuthHandler: BiometricAuthHandler by lazy {
    BiometricAuthHandler(
        biometricAuthenticator = biometricAuthenticator,
        requirement = { AuthenticationRequirement.ENABLED_AND_MANDATORY },
        bypass = { false },
    )
}

//On user action
// Evaluate biometric flow dynamically
when (biometricAuthHandler.evaluate()) {
    BiometricDecision.BYPASS -> {
        // Biometric is turned off or bypassed manually
    }
    BiometricDecision.PROMPT_SKIPPED -> {
        // App not in foreground, or biometric not required in this state
    }
    BiometricDecision.SECURITY_NOT_PRESENT -> {
        // Device doesn't support biometric OR no credential fallback
    }
    BiometricDecision.SETUP_REQUIRED -> {
        // Biometric is supported but user hasn't enrolled — suggest settings intent
    }
    BiometricDecision.AUTHENTICATE -> {
        biometricAuthenticator.authenticate()
    }
}

💳 Mode 2: Transaction-Level Security (Automatic Per-Screen Auth)

Use this when your app needs biometric protection for every screen or session, like banking apps, parental control, or work-profile locked apps.

Biometric prompts auto-trigger as the user navigates the app.

✅ Step 1: Register AppVisibilityTracker (Once)

In your Application or base Activity:

override fun onCreate() {
    super.onCreate()
    ProcessLifecycleOwner.get().lifecycle.addObserver(AppVisibilityTracker)
}

✅ Step 2: Create a `BaseBiometricActivity`

abstract class BaseBiometricActivity : AppCompatActivity() {

    private val biometricAuthenticator: BiometricAuthenticator by lazy {
        val biometricManager = MyBiometricManagerImpl(
            this,
            "Unlock",
            "Unlock to use the app"
        )

        BiometricAuthenticatorImpl(
            biometricManager,
            this
        )
    }

    private val biometricAuthHandler: BiometricAuthHandler by lazy {
        BiometricAuthHandler(
            biometricAuthenticator = biometricAuthenticator,
            requirement = { AuthenticationRequirement.ENABLED_AND_MANDATORY },
            bypass = { false },
        )
    }

    override fun onResume() {
        super.onResume()

        // Evaluate biometric flow dynamically
        when (biometricAuthHandler.evaluate()) {
            BiometricDecision.BYPASS -> {
                // Biometric is turned off or bypassed manually
            }
            BiometricDecision.PROMPT_SKIPPED -> {
                // App not in foreground, or biometric not required in this state
            }
            BiometricDecision.SECURITY_NOT_PRESENT -> {
                // Device doesn't support biometric OR no credential fallback
            }
            BiometricDecision.SETUP_REQUIRED -> {
                // Biometric is supported but user hasn't enrolled — suggest settings intent
            }
            BiometricDecision.AUTHENTICATE -> {
                biometricAuthenticator.authenticate()
            }
        }
    }
}

Then extend it across your app:

class DashboardActivity : BaseBiometricActivity()

🧭 Use Case Table

Use Case	Recommended Mode
Secure a settings/profile page	🔐 Identity Protection (Mode 1)
Authenticate before money transfer	💳 Transaction-Level (Mode 2)
Lock every screen or session	💳 Transaction-Level (Mode 2)