Per RFC 7519 Section 4.1.3, resource servers should only validate their
own presence in the audience claim, not check for other resource servers.
Changes:
- UnifiedTokenVerifier now validates only MCP audience (not Nextcloud's)
- Nextcloud independently validates its own audience when receiving API calls
- This is NOT token passthrough (we validate tokens before use)
- This IS token reuse which is explicitly allowed by RFC 8707
Updates:
- Simplified _validate_multi_audience() to follow OAuth spec
- Updated docstrings and comments to clarify RFC 7519 compliance
- Fixed unit tests that expected dual-audience validation
- Updated ADR-005 to document the correct OAuth interpretation
- All tests pass: unit (65), smoke (5), OAuth integration
This makes the implementation simpler, more maintainable, and properly
aligned with OAuth 2.0 specifications while maintaining security.
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Co-Authored-By: Claude <noreply@anthropic.com>
This ADR addresses the critical token passthrough vulnerability identified
in Issue #261 by proposing a unified token verifier that eliminates the
security issue while maintaining flexibility.
Key changes:
- Consolidates two non-compliant verifiers into single UnifiedTokenVerifier
- Implements two-layer architecture (verification + exchange)
- Supports multi-audience mode (default) and token exchange mode (opt-in)
- Removes all token passthrough paths to comply with MCP security spec
- Works within python-sdk constraints using proper separation of concerns
The solution provides:
- Single source of truth for token validation
- MCP specification compliance
- Minimal performance impact (1-2% of LLM request time)
- Clear migration path for existing deployments
BREAKING CHANGE: All OAuth deployments must be reconfigured to specify
resource URIs (NEXTCLOUD_MCP_SERVER_URL and NEXTCLOUD_RESOURCE_URI) and
choose between multi-audience or token exchange mode.
Related: #261
Supersedes: Token passthrough mode in ADR-004
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Co-Authored-By: Claude <noreply@anthropic.com>
Chris Coutinho