- Add shared Anthropic utilities package with OAuth and API key client creation
- Implement provider-specific message routing alongside existing v1 API
- Enhance authentication middleware with priority handling (API key > Bearer token)
- Add comprehensive auth middleware test suite with timing attack protection
- Update session handling and message transformation for Claude Code integration
- Improve error handling and validation across message processing pipeline
- Standardize import formatting and code structure across affected modules
This establishes the foundation for Claude Code OAuth authentication while maintaining
backward compatibility with existing API key authentication methods.
