# OAuth State Verification Implementation

## Objective
Implement proper OAuth state parameter verification in the callback handler to prevent CSRF attacks. Currently, the state is generated and stored in the session but never verified upon callback.

## Context
The OAuth2 specification requires state verification to prevent cross-site request forgery attacks. In `oauth2_capture/views.py:76-81`, we generate a state parameter and store it in the session, but in the `oauth2_callback` function (lines 17-57), we never verify that the returned state matches what we stored.

**Current Security Gap:**
- State generated: `request.session[f"{provider}_oauth_state"] = state`
- State never verified in callback
- Vulnerable to CSRF attacks where attacker could initiate OAuth flow

## Technical Details

### Implementation Steps
1. **Extract state from callback**: Get state parameter from `request.GET.get("state")`
<<<<<<< HEAD
2. **Retrieve stored state**: Get `request.session.get(f"{provider}_oauth_state")`  
=======
2. **Retrieve stored state**: Get `request.session.get(f"{provider}_oauth_state")`
>>>>>>> faace65 (Add comprehensive OAuth security, testing, and coverage infrastructure)
3. **Verify match**: Compare the two values
4. **Clear session**: Remove stored state after verification
5. **Handle mismatches**: Return appropriate error response

### Code Changes Required
- Modify `oauth2_callback` function in `oauth2_capture/views.py`
- Add state verification before token exchange
- Add proper error handling and logging

## Testing Requirements
1. **Valid State Test**: Verify successful callback with matching state
2. **Invalid State Test**: Verify rejection when state doesn't match
3. **Missing State Test**: Verify rejection when no state provided
4. **Session Cleanup Test**: Verify state is removed from session after use
5. **Multiple Provider Test**: Verify state isolation between providers

## Dependencies
None - this is a standalone security fix.

## Estimated Complexity
Simple (1-2 hours)

## Files to Modify
- `oauth2_capture/views.py`: Modify `oauth2_callback` function (lines 17-57)
- `oauth2_capture/tests/test_views.py`: Create new test file for view testing

## Example Code

```python
def oauth2_callback(request: HttpRequest, provider: str) -> HttpResponse:
    """Finalize the Oauth2 flow with proper state verification."""
<<<<<<< HEAD
    
    # Extract state from callback
    callback_state = request.GET.get("state")
    session_state = request.session.get(f"{provider}_oauth_state")
    
=======

    # Extract state from callback
    callback_state = request.GET.get("state")
    session_state = request.session.get(f"{provider}_oauth_state")

>>>>>>> faace65 (Add comprehensive OAuth security, testing, and coverage infrastructure)
    # Verify state parameter
    if not callback_state or not session_state:
        logger.warning("OAuth callback missing state parameter for provider %s", provider)
        return HttpResponse("Invalid OAuth state - missing parameter", status=400)
<<<<<<< HEAD
    
    if callback_state != session_state:
        logger.warning("OAuth state mismatch for provider %s", provider) 
        return HttpResponse("Invalid OAuth state - verification failed", status=400)
    
    # Clear the state from session
    request.session.pop(f"{provider}_oauth_state", None)
    
=======

    if callback_state != session_state:
        logger.warning("OAuth state mismatch for provider %s", provider)
        return HttpResponse("Invalid OAuth state - verification failed", status=400)

    # Clear the state from session
    request.session.pop(f"{provider}_oauth_state", None)

>>>>>>> faace65 (Add comprehensive OAuth security, testing, and coverage infrastructure)
    # Continue with existing token exchange logic...
    try:
        oauth2_provider = OAuth2ProviderFactory.get_provider(provider)
    except ValueError as e:
        return HttpResponse(str(e), status=400)
<<<<<<< HEAD
    
=======

>>>>>>> faace65 (Add comprehensive OAuth security, testing, and coverage infrastructure)
    # ... rest of existing code
```

## Success Criteria
- [ ] State parameter is properly verified in all OAuth callbacks
- [ ] CSRF attacks are prevented through state validation
- [ ] Appropriate error responses for invalid/missing state
- [ ] Session state is cleaned up after verification
- [ ] Comprehensive test coverage for all scenarios
<<<<<<< HEAD
- [ ] No regression in existing OAuth flows
=======
- [ ] No regression in existing OAuth flows
>>>>>>> faace65 (Add comprehensive OAuth security, testing, and coverage infrastructure)
