Biometric authentication in Android Kotlin

Introduction

Biometric authentication lets users unlock apps using their fingerprint or face. It makes apps safer and easier to use without typing passwords.

Unlocking a banking app quickly and securely.

Allowing access to private notes or files with fingerprint.

Confirming a purchase or payment with face recognition.

Logging into an app without remembering a password.

Protecting sensitive settings or information inside an app.

Syntax

Android Kotlin

val biometricPrompt = BiometricPrompt(this, ContextCompat.getMainExecutor(this),
    object : BiometricPrompt.AuthenticationCallback() {
        override fun onAuthenticationSucceeded(result: BiometricPrompt.AuthenticationResult) {
            super.onAuthenticationSucceeded(result)
            // User authenticated successfully
        }

        override fun onAuthenticationError(errorCode: Int, errString: CharSequence) {
            super.onAuthenticationError(errorCode, errString)
            // Handle error
        }

        override fun onAuthenticationFailed() {
            super.onAuthenticationFailed()
            // Authentication failed
        }
    })

val promptInfo = BiometricPrompt.PromptInfo.Builder()
    .setTitle("Login with Biometrics")
    .setSubtitle("Use your fingerprint or face to login")
    .setNegativeButtonText("Cancel")
    .build()

biometricPrompt.authenticate(promptInfo)

Use BiometricPrompt to show the biometric dialog.

Always provide a negative button for fallback.

Examples

This example shows a basic biometric prompt with title, subtitle, and cancel button.

Android Kotlin

val biometricPrompt = BiometricPrompt(this, ContextCompat.getMainExecutor(this),
    object : BiometricPrompt.AuthenticationCallback() {
        override fun onAuthenticationSucceeded(result: BiometricPrompt.AuthenticationResult) {
            super.onAuthenticationSucceeded(result)
            // Success action
        }

        override fun onAuthenticationError(errorCode: Int, errString: CharSequence) {
            super.onAuthenticationError(errorCode, errString)
            // Error handling
        }

        override fun onAuthenticationFailed() {
            super.onAuthenticationFailed()
            // Failed attempt
        }
    })

val promptInfo = BiometricPrompt.PromptInfo.Builder()
    .setTitle("Biometric login")
    .setSubtitle("Log in using your biometric credential")
    .setNegativeButtonText("Use password")
    .build()

biometricPrompt.authenticate(promptInfo)

Customize the prompt with a description instead of subtitle.

Android Kotlin

val promptInfo = BiometricPrompt.PromptInfo.Builder()
    .setTitle("Secure Access")
    .setDescription("Authenticate to continue")
    .setNegativeButtonText("Cancel")
    .build()

Sample App

This app shows a biometric login prompt when started. It prints messages to the console based on success, failure, or error.

Android Kotlin

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.biometric.BiometricPrompt
import androidx.core.content.ContextCompat

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        val biometricPrompt = BiometricPrompt(this, ContextCompat.getMainExecutor(this),
            object : BiometricPrompt.AuthenticationCallback() {
                override fun onAuthenticationSucceeded(result: BiometricPrompt.AuthenticationResult) {
                    super.onAuthenticationSucceeded(result)
                    println("Authentication succeeded!")
                }

                override fun onAuthenticationError(errorCode: Int, errString: CharSequence) {
                    super.onAuthenticationError(errorCode, errString)
                    println("Authentication error: $errString")
                }

                override fun onAuthenticationFailed() {
                    super.onAuthenticationFailed()
                    println("Authentication failed")
                }
            })

        val promptInfo = BiometricPrompt.PromptInfo.Builder()
            .setTitle("Login with Biometrics")
            .setSubtitle("Use your fingerprint or face to login")
            .setNegativeButtonText("Cancel")
            .build()

        biometricPrompt.authenticate(promptInfo)
    }
}

Important Notes

Test biometric features on a real device with fingerprint or face setup.

Handle cases when biometric hardware is not available or not enrolled.

Always provide a fallback option like PIN or password.

Summary

Biometric authentication improves app security and user convenience.

Use BiometricPrompt to show the system biometric dialog.

Always handle success, failure, and errors gracefully.