Initial Pigeon definition, modified from Android

packages/local_auth/local_auth_ios/pigeons/copyright.txt

@@ -0,0 +1,3 @@
+Copyright 2013 The Flutter Authors. All rights reserved.
+Use of this source code is governed by a BSD-style license that can be
+found in the LICENSE file.

packages/local_auth/local_auth_ios/pigeons/messages.dart

@@ -0,0 +1,101 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:pigeon/pigeon.dart';
+
+@ConfigurePigeon(PigeonOptions(
+  dartOut: 'lib/src/messages.g.dart',
+  objcHeaderOut: 'ios/Classes/messages.g.h',
+  objcSourceOut: 'ios/Classes/messages.g.m',
+  objcOptions: ObjcOptions(
+    prefix: 'FLA',
+  ),
+  copyrightHeader: 'pigeons/copyright.txt',
+))
+
+/// Pigeon version of IOSAuthMessages, plus the authorization reason.
+///
+/// See auth_messages_ios.dart for details.
+class AuthStrings {
+  /// Constructs a new instance.
+  const AuthStrings({
+    required this.reason,
+    required this.lockOut,
+    required this.goToSettingsButton,
+    required this.goToSettingsDescription,
+    required this.cancelButton,
+    required this.localizedFallbackTitle,
+  });
+
+  final String reason;
+  final String lockOut;
+  final String goToSettingsButton;
+  final String goToSettingsDescription;
+  final String cancelButton;
+  final String localizedFallbackTitle;
+}
+
+/// Possible outcomes of an authentication attempt.
+enum AuthResult {
+  /// The user authenticated successfully.
+  success,
+
+  /// The user failed to successfully authenticate.
+  failure,
+
+  /// The authentication system was not available.
+  errorNotAvailable,
+
+  /// No biometrics are enrolled.
+  errorNotEnrolled,
+
+  /// No passcode is set.
+  errorPasscodeNotSet,
+}
+
+class AuthOptions {
+  AuthOptions(
+      {required this.biometricOnly,
+      required this.sticky,
+      required this.useErrorDialgs});
+  final bool biometricOnly;
+  final bool sticky;
+  final bool useErrorDialgs;
+}
+
+// TODO(stuartmorgan): Remove this when
+// https://github.com/flutter/flutter/issues/87307 is implemented.
+class AuthResultWrapper {
+  AuthResultWrapper({required this.value});
+  final AuthResult value;
+}
+
+/// Pigeon equivalent of the subset of BiometricType used by iOS.
+enum AuthBiometrics { weak, strong }
+
+// TODO(stuartmorgan): Remove this when
+// https://github.com/flutter/flutter/issues/87307 is implemented.
+class AuthClassificationWrapper {
+  AuthClassificationWrapper({required this.value});
+  final AuthBiometrics value;
+}
+
+@HostApi()
+abstract class LocalAuthApi {
+  /// Returns true if this device supports authentication.
+  bool isDeviceSupported();
+
+  /// Returns true if this device can support biometric authentication, whether
+  /// any biometrics are enrolled or not.
+  bool deviceCanSupportBiometrics();
+
+  /// Returns the biometric types that are enrolled, and can thus be used
+  /// without additional setup.
+  List<AuthClassificationWrapper> getEnrolledBiometrics();
+
+  /// Attempts to authenticate the user with the provided [options], and using
+  /// [strings] for any UI.
+  @async
+  AuthResultWrapper authenticate(AuthOptions options, AuthStrings strings);
+}

packages/local_auth/local_auth_ios/pubspec.yaml

@@ -23,5 +23,7 @@ dependencies:
   local_auth_platform_interface: ^1.0.1
 
 dev_dependencies:
+  build_runner: ^2.3.3
   flutter_test:
     sdk: flutter
+  pigeon: ^9.2.4