Biometric Authentication

Checking for support

You should check if the current device supports authentication by biometrics by calling the canAuthenticateWithBiometryType function:

if (LocalAuth.service.canAuthenticateWithBiometryType())
// Biometric authentication is available

You can also check for the individual biometry types, for example, to check if fingerprint authentication is available:

if (LocalAuth.service.canAuthenticateWithBiometryType( BiometryType.FINGERPRINT ))
// Fingerprint authentication is available

This function checks a range of conditions to ensure that you can use biometric authentication on the user's device including:

  • user has set a passcode
  • user has scanned some fingerprints
  • you have set appropriate permissions (manifest additions)

Note: Most devices support fingerprint or face biometric authentication and not both.


Authenticating via fingerprint is as simple as calling the authenticateWithBiometryType function and registering your event listeners.

The authenticateWithBiometryType function requires a reason which is a message that will be displayed to the user to explain the reason you are asking for authentication.

LocalAuth.service.addEventListener( LocalAuthEvent.AUTH_SUCCESS, authSuccessHandler );
LocalAuth.service.addEventListener( LocalAuthEvent.AUTH_FAILED, authFailedHandler );
LocalAuth.service.authenticateWithBiometryType( "Unlock access to locked feature" );

Then in your event listeners:

function authSuccessHandler( event:LocalAuthEvent ):void
trace( "localAuth_authSuccessHandler" );
function authFailedHandler( event:LocalAuthEvent ):void
trace( "localAuth_authFailedHandler: " + event.errorCode + "::" +event.message );

The AUTH_SUCCESS event will be fired only if the user successfully authenticates using their fingerprint.

In all other cases the AUTH_FAILED event is dispatched and you should respond by processing the errorCode appropriately. The error codes are defined in the LocalAuthError class. For example if the user cancels the authentication the LocalAuthError.USER_CANCEL code will be returned.

An important code to process is the LocalAuthError.USER_FALLBACK. This is received when the user has pressed the Enter Password option in the dialog after failing to scan a fingerprint once. You should respect this decision and provide the ability for the user to authenticate using your normal method.

You can also specify the biometry type to be used if you require:

"Unlock access to locked feature",

Note: specifying the biometry type may return false when the biometry type is not supported

Cancel Authentication

If you wish to programatically cancel the authentication process you can call cancelAuthenticate.


After calling this you should receive an AUTH_FAILED event to indicate the failure of the authentication process (if an authentication process was occurring at the time).