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This is documentation for the next SDK version. For up-to-date documentation, see the latest version (SDK 52).

Expo LocalAuthentication iconExpo LocalAuthentication

GitHub

npm

A library that provides functionality for implementing the Fingerprint API (Android) or FaceID and TouchID (iOS) to authenticate the user with a face or fingerprint scan.

Android
iOS

expo-local-authentication allows you to use the Biometric Prompt (Android) or FaceID and TouchID (iOS) to authenticate the user with a fingerprint or face scan.

Installation

Terminal
- npx expo install expo-local-authentication

If you are installing this in an existing React Native app, start by installing expo in your project. Then, follow the additional instructions as mentioned by the library's README under "Installation in bare React Native projects" section.

Configuration in app.json/app.config.js

You can configure expo-local-authentication using its built-in config plugin if you use config plugins in your project (EAS Build or npx expo run:[android|ios]). The plugin allows you to configure various properties that cannot be set at runtime and require building a new app binary to take effect.

Example app.json with config plugin

app.json
{
  "expo": {
    "plugins": [
      [
        "expo-local-authentication",
        {
          "faceIDPermission": "Allow $(PRODUCT_NAME) to use Face ID."
        }
      ]
    ]
  }
}

Configurable properties

NameDefaultDescription
faceIDPermission"Allow $(PRODUCT_NAME) to use Face ID"
Only for: 
iOS

A string to set the NSFaceIDUsageDescription permission message.

Are you using this library in a bare React Native app?

Learn how to configure the native projects in the installation instructions in the expo-local-authentication repository.

API

import * as LocalAuthentication from 'expo-local-authentication';

Methods

Android
iOS

LocalAuthentication.authenticateAsync(options)

ParameterType
options
(optional)		LocalAuthenticationOptions

Attempts to authenticate via Fingerprint/TouchID (or FaceID if available on the device).

Note: Apple requires apps which use FaceID to provide a description of why they use this API. If you try to use FaceID on an iPhone with FaceID without providing infoPlist.NSFaceIDUsageDescription in app.json, the module will authenticate using device passcode. For more information about usage descriptions on iOS, see permissions guide.

Returns:

Promise<LocalAuthenticationResult>

Returns a promise which fulfils with LocalAuthenticationResult.

Android

LocalAuthentication.cancelAuthenticate()

Cancels authentication flow.

Returns:

Promise<void>

Android
iOS

LocalAuthentication.getEnrolledLevelAsync()

Determine what kind of authentication is enrolled on the device.

Returns:

Promise<SecurityLevel>

Returns a promise which fulfils with SecurityLevel.

Note: On Android devices prior to M, SECRET can be returned if only the SIM lock has been enrolled, which is not the method that authenticateAsync prompts.

Android
iOS

LocalAuthentication.hasHardwareAsync()

Determine whether a face or fingerprint scanner is available on the device.

Returns:

Promise<boolean>

Returns a promise which fulfils with a boolean value indicating whether a face or fingerprint scanner is available on this device.

Android
iOS

LocalAuthentication.isEnrolledAsync()

Determine whether the device has saved fingerprints or facial data to use for authentication.

Returns:

Promise<boolean>

Returns a promise which fulfils to boolean value indicating whether the device has saved fingerprints or facial data for authentication.

Android
iOS

LocalAuthentication.supportedAuthenticationTypesAsync()

Determine what kinds of authentications are available on the device.

Returns:

Promise<AuthenticationType[]>

Returns a promise which fulfils to an array containing AuthenticationTypes.

Devices can support multiple authentication methods- i.e. [1,2] means the device supports both fingerprint and facial recognition. If none are supported, this method returns an empty array.

Types

Android

BiometricsSecurityLevel

Literal Type: string

Security level of the biometric authentication to allow.

Acceptable values are: 'weak' | 'strong'

Android
iOS

LocalAuthenticationOptions

NameTypeDescription
biometricsSecurityLevel
(optional)		BiometricsSecurityLevel
Only for: 
Android

Sets the security class of biometric authentication to allow. strong allows only Android Class 3 biometrics. For example, a fingerprint or a 3D face scan. weak allows both Android Class 3 and Class 2 biometrics. Class 2 biometrics are less secure than Class 3. For example, a camera-based face unlock.

Default:'weak'
cancelLabel
(optional)		string

Allows to customize the default Cancel label shown.

disableDeviceFallback
(optional)		boolean

After several failed attempts the system will fallback to the device passcode. This setting allows you to disable this option and instead handle the fallback yourself. This can be preferable in certain custom authentication workflows. This behaviour maps to using the iOS LAPolicyDeviceOwnerAuthenticationWithBiometrics policy rather than the LAPolicyDeviceOwnerAuthentication policy. Defaults to false.

fallbackLabel
(optional)		string
Only for: 
iOS

Allows to customize the default Use Passcode label shown after several failed authentication attempts. Setting this option to an empty string disables this button from showing in the prompt.

promptMessage
(optional)		string

A message that is shown alongside the TouchID or FaceID prompt.

requireConfirmation
(optional)		boolean
Only for: 
Android

Sets a hint to the system for whether to require user confirmation after authentication. This may be ignored by the system if the user has disabled implicit authentication in Settings or if it does not apply to a particular biometric modality. Defaults to true.

Android
iOS

LocalAuthenticationResult

Type: object shaped as below:


NameTypeDescription
successtrue-

NameTypeDescription
errorstring-
successfalse-
warning
(optional)		string-

Enums

Android
iOS

AuthenticationType

AuthenticationType Values

FINGERPRINT

AuthenticationType.FINGERPRINT ＝ 1

Indicates fingerprint support.

FACIAL_RECOGNITION

AuthenticationType.FACIAL_RECOGNITION ＝ 2

Indicates facial recognition support.

Only for: 
Android

IRIS

AuthenticationType.IRIS ＝ 3

Indicates iris recognition support.

Android
iOS

SecurityLevel

SecurityLevel Values

NONE

SecurityLevel.NONE ＝ 0

Indicates no enrolled authentication.

SECRET

SecurityLevel.SECRET ＝ 1

Indicates non-biometric authentication (e.g. PIN, Pattern).

BIOMETRIC_WEAK

SecurityLevel.BIOMETRIC_WEAK ＝ 2

Indicates weak biometric authentication. For example, a 2D image-based face unlock.

There are currently no weak biometric authentication options on iOS.

BIOMETRIC_STRONG

SecurityLevel.BIOMETRIC_STRONG ＝ 3

Indicates strong biometric authentication. For example, a fingerprint scan or 3D face unlock.

Permissions

Android

The following permissions are added automatically through this library's AndroidManifest.xml:

Android PermissionDescription

USE_BIOMETRIC

Allows an app to use device supported biometric modalities.

USE_FINGERPRINT

This constant was deprecated in API level 28. Applications should request USE_BIOMETRIC instead

iOS

The following usage description keys are used by this library:

Info.plist KeyDescription

NSFaceIDUsageDescription

A message that tells the user why the app is requesting the ability to authenticate with Face ID.