This PR fixes multiple OAuth-related issues:
## Unified OAuth Callback
- Consolidated `/oauth/callback-nextcloud` and `/oauth/login-callback` into single `/oauth/callback` endpoint
- Flow type determined by session lookup via state parameter (no query params in redirect_uri)
- Fixes redirect_uri validation issues with IdPs requiring exact match
- Legacy endpoints kept as aliases for backwards compatibility
## PKCE Implementation
- Implemented PKCE (RFC 7636) for Flow 2 (resource provisioning)
- Generate code_verifier and code_challenge
- Store code_verifier in session storage
- Retrieve and use in token exchange
- Fixed PKCE for browser login (integrated mode)
- Previously only worked for external IdP (Keycloak)
- Now works for both Nextcloud OIDC and external IdP
## Login Elicitation Fixes (ADR-006)
- Fixed elicitation URL to route through MCP server endpoint
- Changed from direct Nextcloud URL to `/oauth/authorize-nextcloud`
- Ensures PKCE is properly handled by server
- Fixed login detection after OAuth flow completes
- Look up refresh token by state parameter instead of user_id
- Works even when Flow 1 token not present
- Added `get_refresh_token_by_provisioning_client_id()` method
## Session Authentication
- Fixed `/user/page` redirect loop
- Shared oauth_context with mounted browser_app
- SessionAuthBackend can now validate sessions correctly
## Tests
- Added comprehensive login elicitation test suite
- Updated scope authorization test expectations
- All 43 OAuth tests passing
## Files Changed
- `app.py`: Shared oauth_context, unified callback route
- `oauth_routes.py`: Unified callback, PKCE for Flow 2
- `browser_oauth_routes.py`: PKCE for integrated mode
- `oauth_tools.py`: Fixed elicitation URL generation
- `refresh_token_storage.py`: Added lookup by provisioning_client_id
- `test_login_elicitation.py`: New test suite
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
Chris Coutinho
0c9a9ea24d