- Add is_oauth and oauth_provider fields to ProviderSpec
- Update _make_provider() to use registry for OAuth provider detection
- Update get_provider() to support OAuth providers (no API key required)
- Mark OpenAI Codex as OAuth-based provider in registry
This improves the provider registry architecture to support OAuth-based
authentication flows, making it extensible for future OAuth providers.
Benefits:
- OAuth providers are now registry-driven (not hardcoded)
- Extensible design: new OAuth providers only need registry entry
- Backward compatible: existing API key providers unaffected
- Clean separation: OAuth logic centralized in registry
- Add OpenAI Codex ProviderSpec to registry.py
- Add openai_codex config field to ProvidersConfig in schema.py
- Mark Codex as OAuth-based (no API key required)
- Set appropriate default_api_base for Codex API
This integrates the Codex OAuth provider with the refactored
provider registry system introduced in upstream commit 299d8b3.
pinhua33