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Expo LocalAuthentication

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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.

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.

Platform Compatibility

Android Device	Android Emulator	iOS Device	iOS Simulator	Web

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

Name	Default	Description
`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

`LocalAuthentication.authenticateAsync(options)`

Parameter	Type
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.

`LocalAuthentication.cancelAuthenticate()`

Only for:

Android

Cancels authentication flow.

Returns:

Promise<void>

`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.

`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.

`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.

`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

`LocalAuthenticationOptions`

Name	Type	Description
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`.

`LocalAuthenticationResult`

Type: object shaped as below:

Name	Type	Description
success	`true`	-

Name	Type	Description
error	`string`	-
success	`false`	-
warning (optional)	`string`	-

Enums

`AuthenticationType`

`FINGERPRINT`

AuthenticationType.FINGERPRINT ＝ 1

Indicates fingerprint support.

`FACIAL_RECOGNITION`

AuthenticationType.FACIAL_RECOGNITION ＝ 2

Indicates facial recognition support.

`IRIS`

Only for:

Android

AuthenticationType.IRIS ＝ 3

Indicates iris recognition support.

`SecurityLevel`

`NONE`

SecurityLevel.NONE ＝ 0

Indicates no enrolled authentication.

`SECRET`

SecurityLevel.SECRET ＝ 1

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

`BIOMETRIC`

SecurityLevel.BIOMETRIC ＝ 2

Indicates biometric authentication.

Permissions

Android

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

Android Permission	Description
`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 Key	Description
`NSFaceIDUsageDescription`	A message that tells the user why the app is requesting the ability to authenticate with Face ID.