Service account tokens (client_credentials grant) violate OAuth "act on-behalf-of"
principles and have been moved to ADR-002's "Will Not Implement" section.
## Problem Discovery
Testing revealed that service account tokens create Nextcloud user accounts
(e.g., `service-account-nextcloud-mcp-server`) due to user_oidc's bearer
provisioning feature. This violates core OAuth principles:
- ❌ Creates stateful server identity in Nextcloud
- ❌ All actions attributed to service account, not real user
- ❌ Breaks audit trail and user attribution
- ❌ Service account becomes "admin by another name"
## Changes
### Documentation (ADR-002)
- Moved service account (old Tier 1) to "Will Not Implement" section
- Added "OAuth Act On-Behalf-Of Principle" section
- Renumbered tiers:
- Tier 1: Impersonation (NOT IMPLEMENTED)
- Tier 2: Delegation via token exchange (IMPLEMENTED)
- Updated status to reflect rejection of service accounts
### Code Warnings
- Added comprehensive warning to KeycloakOAuthClient.get_service_account_token()
- Clarified VALID use: only as subject_token for RFC 8693 token exchange
- Clarified INVALID use: direct API access with service account token
### Supporting Documentation
- CLAUDE.md: Removed outdated "Tier 1" references, added rejection note
- oauth-impersonation-findings.md: Added prominent update banner
- audience-validation-setup.md: Updated tier numbers, added rejection note
- tests/manual/test_token_exchange.py: Added warning comment
## Valid Patterns (ADR-002)
✅ Foreground operations: User's access token from MCP request
✅ Background operations: Token exchange (impersonation/delegation)
✅ Offline access: Refresh tokens with user consent
❌ Service accounts: Creates independent server identity (REJECTED)
## Alternative
If service account pattern is truly needed, use BasicAuth mode instead of
OAuth mode. OAuth mode MUST maintain "act on-behalf-of" semantics.
Related: c12df98 (revert of service account test)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
Remove file-based caching of OAuth client credentials and implement automatic
client lifecycle management for test fixtures.
Changes:
- Add RFC 7592 client deletion function in auth/client_registration.py
- Remove cache_file parameter from _create_oauth_client_with_scopes helper
- Update all OAuth credential fixtures to use yield/finalizer pattern
- Add automatic client cleanup at end of test session (best-effort)
- Remove persistent .nextcloud_oauth_*.json cache files
Benefits:
- No persistent cache files cluttering repository
- Fresh OAuth clients created for each test session via DCR
- Automatic cleanup attempts (RFC 7592 DELETE endpoint)
- Cleaner test environment with proper fixture lifecycle
Note: Client deletion may fail due to Nextcloud authentication middleware
(logged as warning). The key improvement is removing persistent cache files.
OAuth clients may accumulate in Nextcloud but can be cleaned manually.
Chris Coutinho