Oauth - GitHub OAuth Provider (Web Flow + Deep Link)

[coderabbitai]

Problem

GitHub OAuth via browser with CSRF state and deep-link callback is not implemented.

Scope

Implement GitHubOAuthProvider to:

• Generate and store state
• Launch external browser authorize URL
• Return null (the code arrives via deep link handler)

Approach

Use url_launcher and shared_preferences.

Dependencies

• Blocked By:
• Blocks:

Files to Modify/Create

• talawa/lib/services/oauth/providers/github_oauth_provider.dart

Acceptance Criteria

• All existing functionality must be maintained
• Implementation must ensure no breaking changes when PR is merged

Testing Requirements

• All tests must pass successfully
• Code coverage must be >= 96%

Sample Code

This sample code is only representative of what could be done. It is provided only to give a general outline. You will need to use your initiative and industry best practices to find a solution that is suitable for the application.

// talawa/lib/services/oauth/providers/github_oauth_provider.dart
import 'dart:convert'; import 'dart:math';
import 'package:url_launcher/url_launcher.dart';
import 'package:shared_preferences/shared_preferences.dart';
import '../../oauth_provider.dart';

class GitHubOAuthProviderImpl implements OAuthProvider {
  @override String get providerName => "GITHUB";

  Future<String> _genState() async {
    final b = List<int>.generate(32, (_) => Random.secure().nextInt(256));
    return base64UrlEncode(b);
  }

  @override Future<String?> authorize() async {
    final prefs = await SharedPreferences.getInstance();
    final state = await _genState();
    await prefs.setString('gh_oauth_state', state);
    final clientId = const String.fromEnvironment('GITHUB_CLIENT_ID', defaultValue: '');
    final redirect = const String.fromEnvironment('GITHUB_REDIRECT_URI', defaultValue: 'talawa://oauth/callback');
    final uri = Uri.https("github.com", "/login/oauth/authorize", {
      "client_id": clientId, "redirect_uri": redirect, "scope": "user:email", "state": state
    });
    await launchUrl(uri, mode: LaunchMode.externalApplication);
    return null;
  }
}