feat: Implement OAuth2 authentication with Google and GitHub

- Added OAuth2 endpoints for Google and GitHub authentication.
- Created OAuth service to handle provider interactions and user info retrieval.
- Implemented user OAuth repository for managing user OAuth links in the database.
- Updated auth service to support linking existing users and creating new users via OAuth.
- Added CORS middleware to allow frontend access.
- Created tests for OAuth endpoints and service functionality.
- Introduced environment configuration for OAuth client IDs and secrets.
- Added logging for OAuth operations and error handling.

tests/services/test_oauth_service.py

@@ -0,0 +1,192 @@
+"""Tests for OAuth service."""
+
+from typing import Any
+from unittest.mock import AsyncMock, Mock, patch
+
+import pytest
+from httpx import AsyncClient
+
+from app.services.oauth import (
+    GitHubOAuthProvider,
+    GoogleOAuthProvider,
+    OAuthService,
+    OAuthUserInfo,
+)
+
+
+class TestOAuthService:
+    """Test OAuth service functionality."""
+
+    @pytest.mark.asyncio
+    async def test_oauth_service_initialization(self, test_session: Any) -> None:
+        """Test OAuth service initialization."""
+        oauth_service = OAuthService(test_session)
+
+        assert "google" in oauth_service.providers
+        assert "github" in oauth_service.providers
+        assert isinstance(oauth_service.providers["google"], GoogleOAuthProvider)
+        assert isinstance(oauth_service.providers["github"], GitHubOAuthProvider)
+
+    @pytest.mark.asyncio
+    async def test_generate_state(self, test_session: Any) -> None:
+        """Test state generation."""
+        oauth_service = OAuthService(test_session)
+        state = oauth_service.generate_state()
+
+        assert isinstance(state, str)
+        assert len(state) > 10  # Should be a reasonable length
+        
+        # Generate another to ensure they're different
+        state2 = oauth_service.generate_state()
+        assert state != state2
+
+    @pytest.mark.asyncio
+    async def test_get_provider_valid(self, test_session: Any) -> None:
+        """Test getting valid OAuth provider."""
+        oauth_service = OAuthService(test_session)
+
+        google_provider = oauth_service.get_provider("google")
+        assert isinstance(google_provider, GoogleOAuthProvider)
+        assert google_provider.provider_name == "google"
+
+        github_provider = oauth_service.get_provider("github")
+        assert isinstance(github_provider, GitHubOAuthProvider)
+        assert github_provider.provider_name == "github"
+
+    @pytest.mark.asyncio
+    async def test_get_provider_invalid(self, test_session: Any) -> None:
+        """Test getting invalid OAuth provider."""
+        oauth_service = OAuthService(test_session)
+
+        with pytest.raises(Exception) as exc_info:
+            oauth_service.get_provider("invalid")
+        
+        assert "Unsupported OAuth provider" in str(exc_info.value)
+
+    @pytest.mark.asyncio
+    async def test_get_authorization_url(self, test_session: Any) -> None:
+        """Test authorization URL generation."""
+        oauth_service = OAuthService(test_session)
+        state = "test_state_123"
+
+        # Test Google
+        google_url = oauth_service.get_authorization_url("google", state)
+        assert "accounts.google.com" in google_url
+        assert "client_id=" in google_url
+        assert f"state={state}" in google_url
+
+        # Test GitHub
+        github_url = oauth_service.get_authorization_url("github", state)
+        assert "github.com" in github_url
+        assert "client_id=" in github_url
+        assert f"state={state}" in github_url
+
+
+class TestGoogleOAuthProvider:
+    """Test Google OAuth provider."""
+
+    def test_provider_properties(self) -> None:
+        """Test Google provider properties."""
+        provider = GoogleOAuthProvider("test_client_id", "test_secret")
+
+        assert provider.provider_name == "google"
+        assert "accounts.google.com" in provider.authorization_url
+        assert "oauth2.googleapis.com" in provider.token_url
+        assert "googleapis.com" in provider.user_info_url
+        assert "openid email profile" in provider.scope
+
+    def test_authorization_url_generation(self) -> None:
+        """Test authorization URL generation."""
+        provider = GoogleOAuthProvider("test_client_id", "test_secret")
+        state = "test_state"
+
+        auth_url = provider.get_authorization_url(state)
+        
+        assert "accounts.google.com" in auth_url
+        assert "client_id=test_client_id" in auth_url
+        assert f"state={state}" in auth_url
+        assert "scope=openid+email+profile" in auth_url
+
+    @pytest.mark.asyncio
+    async def test_get_user_info_success(self) -> None:
+        """Test successful user info retrieval."""
+        provider = GoogleOAuthProvider("test_client_id", "test_secret")
+        
+        mock_response_data = {
+            "id": "google_user_123",
+            "email": "test@gmail.com",
+            "name": "Test User",
+            "picture": "https://example.com/avatar.jpg",
+        }
+
+        with patch("httpx.AsyncClient.get") as mock_get:
+            mock_response = Mock()
+            mock_response.status_code = 200
+            mock_response.json.return_value = mock_response_data
+            mock_get.return_value = mock_response
+
+            user_info = await provider.get_user_info("test_access_token")
+
+            assert user_info.provider == "google"
+            assert user_info.provider_user_id == "google_user_123"
+            assert user_info.email == "test@gmail.com"
+            assert user_info.name == "Test User"
+            assert user_info.picture == "https://example.com/avatar.jpg"
+
+
+class TestGitHubOAuthProvider:
+    """Test GitHub OAuth provider."""
+
+    def test_provider_properties(self) -> None:
+        """Test GitHub provider properties."""
+        provider = GitHubOAuthProvider("test_client_id", "test_secret")
+
+        assert provider.provider_name == "github"
+        assert "github.com" in provider.authorization_url
+        assert "github.com" in provider.token_url
+        assert "api.github.com" in provider.user_info_url
+        assert "user:email" in provider.scope
+
+    @pytest.mark.asyncio
+    async def test_get_user_info_success(self) -> None:
+        """Test successful user info retrieval."""
+        provider = GitHubOAuthProvider("test_client_id", "test_secret")
+        
+        mock_user_data = {
+            "id": 123456,
+            "login": "testuser",
+            "name": "Test User",
+            "avatar_url": "https://github.com/avatar.jpg",
+        }
+        
+        mock_emails_data = [
+            {"email": "test@example.com", "primary": True, "verified": True},
+            {"email": "secondary@example.com", "primary": False, "verified": True},
+        ]
+
+        with patch("httpx.AsyncClient.get") as mock_get:
+            # Mock user profile response
+            mock_user_response = Mock()
+            mock_user_response.status_code = 200
+            mock_user_response.json.return_value = mock_user_data
+
+            # Mock emails response  
+            mock_emails_response = Mock()
+            mock_emails_response.status_code = 200
+            mock_emails_response.json.return_value = mock_emails_data
+
+            # Return different responses based on URL
+            def side_effect(url, **kwargs):
+                if "user/emails" in str(url):
+                    return mock_emails_response
+                return mock_user_response
+
+            mock_get.side_effect = side_effect
+
+            user_info = await provider.get_user_info("test_access_token")
+
+            assert user_info.provider == "github"
+            assert user_info.provider_user_id == "123456"
+            assert user_info.email == "test@example.com"
+            assert user_info.name == "Test User"
+            assert user_info.picture == "https://github.com/avatar.jpg"