Implement PKCE (Proof Key for Code Exchange) for OIDC authentication to enable
support for public clients and improve OAuth security.
Changes:
- Add oauth/pkce.py with code_verifier generation and S256/plain challenge methods
- Extend OAuthService to support extra auth/token params and public clients (no client_secret)
- Implement PKCE in OIDCLoginService with code_verifier token exchange
- Store PKCE verifier in session during auth initiation (endpoints/api/user.py)
- Add get_pkce_code_verifier() helper with defensive type checking
* Encapsulates pkce_enabled check and session data extraction
* Uses isinstance(data, dict) for safe type validation
* Centralizes logic across OAuth callbacks (callback, attach, cli)
- Include example Keycloak PKCE config in local-dev/stack/config.yaml
Security improvements:
- PKCE method validation to fail fast on invalid configuration
- Defensive session data validation in OAuth callbacks
- Explicit Content-Type headers for form-encoded OAuth requests
- Optimized non-verified JWT decode (skips unnecessary key fetching)
- Exponential backoff for token exchange retries (0.5s, 1.0s, 2.0s)
Configuration:
- PKCE is opt-in via USE_PKCE config (default: disabled)
- OIDC_SERVER must end with trailing slash
- Use host.containers.internal with podman for local dev
Co-authored-by: Claude <noreply@anthropic.com>
