Add Apple signIn support

README.md

@@ -9,6 +9,7 @@ This package enables Firebase OAuth on desktop platforms via webview
 ## Supported providers:
 
 - Google
+- Apple
 - Facebook
 - Twitter
 
@@ -95,7 +96,38 @@ try {
 ```dart
 import 'package:firebase_auth/firebase_auth.dart';
 
-final credential = GoogleAuthProvider.credential(accessToken: result.accessToken)
+final credential = GoogleAuthProvider.credential(accessToken: result.accessToken);
 
 FirebaseAuth.instance.signInWithCredential(credential);
 ```
+
+
+- Example of Apple auth 
+- For Windows platform use firebase_auth version 5.1.4 or later. [PR#13086](https://github.com/firebase/flutterfire/pull/13086)
+
+```dart
+import 'package:desktop_webview_auth/desktop_webview_auth.dart';
+import 'package:desktop_webview_auth/apple.dart';
+import 'package:firebase_auth/firebase_auth.dart';  
+
+final args = AppleSignInArgs(
+    clientId: "your-service-id", //Services ID used as the web application identifier
+    redirectUri: "https://your-project.firebaseapp.com/__/auth/handler",
+);
+
+try {
+    final result = await DesktopWebviewAuth.signIn(args);
+    if (result == null || result.idToken == null) {
+      throw Exception("Authorize process terminated");
+    }
+} catch (err) {
+    // something went wrong
+}
+
+final credential = OAuthProvider("apple.com").credential(
+    idToken: result.idToken!,
+    rawNonce: args.nonce,
+);
+
+FirebaseAuth.instance.signInWithCredential(credential);
+```

lib/apple.dart

@@ -0,0 +1,81 @@
+import 'dart:convert';
+
+import 'package:crypto/crypto.dart';
+
+import 'src/provider_args.dart';
+import 'src/util.dart';
+
+const _defaultSignInScope = '';
+
+/// @see https://developer.apple.com/documentation/sign_in_with_apple/request_an_authorization_to_the_sign_in_with_apple_server
+///
+/// [scope] The amount of user information requested from Apple.
+///   Valid values are name and email. You can request one, both, or none.
+///   Use space separation and percent-encoding for multiple scopes;
+///   for example, "scope=name%20email".
+///
+/// [responseType] The type of response requested. Valid values are
+///   code and id_token. You can request only code, or both code and id_token.
+///   Requesting only id_token is unsupported. When requesting id_token,
+///   [responseMode] must be either fragment or form_post.
+///
+/// [responseMode] The type of response mode expected. Valid values are query,
+///   fragment, and form_post.
+///   If you requested any [scope]s, the value must be form_post.
+///   Note! Firebase auth support only fragment mode, so [scope] must be empty
+///
+/// [nonce] Auto generated, but need for using in
+///   Firebase AppleAuthProvider.credentialWithIDToken, see example below.
+///
+/// ###Example of using with Firebase Auth:
+///
+///     final args = AppleSignInArgs(
+///       clientId: "my-services-id", //Services ID used as the web application identifier
+///       redirectUri: "https://your-project.firebaseapp.com/__/auth/handler",
+///     );
+///
+///     final result = await DesktopWebviewAuth.signIn(args);
+///     if (result == null || result.idToken == null) {
+///       throw Exception("Authorize process terminated");
+///     }
+///
+///     final credential = OAuthProvider("apple.com").credential(idToken: result.idToken!, rawNonce: args.nonce);
+///     FirebaseAuth.instance.signInWithCredential(credential);
+///
+class AppleSignInArgs extends ProviderArgs {
+  final String clientId;
+  final String scope;
+  final String responseType;
+  final String responseMode;
+  final String nonce;
+
+  @override
+  final String redirectUri;
+
+  @override
+  final host = 'appleid.apple.com';
+
+  @override
+  final path = '/auth/authorize';
+
+  AppleSignInArgs({
+    required this.clientId,
+    required this.redirectUri,
+    this.scope = _defaultSignInScope,
+    this.responseType = 'code id_token',
+    this.responseMode = 'fragment',
+    String? nonce,
+  }) : nonce = nonce ?? generateNonce();
+
+  @override
+  Map<String, String> buildQueryParameters() {
+    return {
+      'client_id': clientId,
+      'scope': scope,
+      'response_type': responseType,
+      'response_mode': responseMode,
+      'redirect_uri': redirectUri,
+      'nonce': sha256.convert(utf8.encode(nonce)).toString(),
+    };
+  }
+}