Add new claims to the discovery endpoint
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Dan Milne
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docs/claude-review.md
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docs/claude-review.md
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# Clinch - Independent Code Review
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**Reviewer:** Claude (Anthropic)
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**Review Date:** December 2024
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**Codebase Version:** Commit 4f31fad
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**Review Type:** Security-focused OIDC/OAuth2 correctness review with full application assessment
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---
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## Executive Summary
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Clinch is a self-hosted identity and SSO portal built with Ruby on Rails. This review examined the complete codebase with particular focus on the OIDC/OAuth2 implementation, comparing it against production-grade reference implementations (Rodauth-OAuth, Authelia, Authentik).
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**Overall Assessment: Production-Ready**
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The implementation demonstrates solid security practices, proper adherence to OAuth 2.0 and OpenID Connect specifications, and comprehensive test coverage. The codebase is well-structured, readable, and maintainable.
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---
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## Feature Overview
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### Authentication Methods
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| Feature | Status | Notes |
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|---------|--------|-------|
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| Password Authentication | Implemented | bcrypt hashing, rate-limited |
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| WebAuthn/Passkeys | Implemented | FIDO2 compliant, clone detection |
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| TOTP 2FA | Implemented | With backup codes, admin enforcement |
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| Session Management | Implemented | Device tracking, revocation |
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### SSO Protocols
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| Protocol | Status | Notes |
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|----------|--------|-------|
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| OpenID Connect | Implemented | Full OIDC Core compliance |
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| OAuth 2.0 | Implemented | Authorization Code + Refresh Token grants |
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| ForwardAuth | Implemented | Traefik/Caddy/nginx compatible |
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### User & Access Management
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| Feature | Status | Notes |
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|---------|--------|-------|
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| User CRUD | Implemented | Invitation flow, status management |
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| Group Management | Implemented | With custom claims |
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| Application Management | Implemented | OIDC + ForwardAuth types |
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| Group-based Access Control | Implemented | Per-application restrictions |
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---
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## OIDC/OAuth2 Implementation Review
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### Specification Compliance
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| Specification | Status | Evidence |
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|---------------|--------|----------|
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| RFC 6749 (OAuth 2.0) | Compliant | Proper auth code flow, client authentication |
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| RFC 7636 (PKCE) | Compliant | S256 and plain methods, enforced for public clients |
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| RFC 7009 (Token Revocation) | Compliant | Always returns 200 OK, prevents scanning |
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| OpenID Connect Core 1.0 | Compliant | All required claims, proper JWT structure |
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| OIDC Discovery | Compliant | `.well-known/openid-configuration` |
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| OIDC Back-Channel Logout | Compliant | Logout tokens per spec |
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### ID Token Claims
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The implementation includes all required and recommended OIDC claims:
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```
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Standard: iss, sub, aud, exp, iat, nonce
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Profile: email, email_verified, preferred_username, name
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Security: at_hash, auth_time, acr, azp
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Custom: groups, plus arbitrary claims from groups/users/apps
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```
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### Token Security
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| Aspect | Implementation | Assessment |
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|--------|----------------|------------|
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| Authorization Codes | HMAC-SHA256 hashed, 10-min expiry, single-use | Secure |
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| Access Tokens | HMAC-SHA256 hashed, configurable TTL, indexed lookup | Secure |
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| Refresh Tokens | HMAC-SHA256 hashed, rotation with family tracking | Secure |
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| ID Tokens | RS256 signed JWTs | Secure |
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### Security Features
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1. **Authorization Code Reuse Prevention**
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- Pessimistic database locking prevents race conditions
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- Code reuse triggers revocation of all tokens from that code
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- Location: `oidc_controller.rb:342-364`
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2. **Refresh Token Rotation**
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- Old refresh tokens revoked on use
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- Token family tracking detects stolen token reuse
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- Revoked token reuse triggers family-wide revocation
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- Location: `oidc_controller.rb:504-513`
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3. **PKCE Enforcement**
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- Required for all public clients
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- Configurable for confidential clients
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- Proper S256 challenge verification
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- Location: `oidc_controller.rb:749-814`
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4. **Pairwise Subject Identifiers**
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- Each user gets a unique `sub` per application
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- Prevents cross-application user tracking
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- Location: `oidc_user_consent.rb:59-61`
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---
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## Security Assessment
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### Strengths
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1. **Token Storage Architecture**
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- All tokens (auth codes, access, refresh) are HMAC-hashed before storage
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- Database compromise does not reveal usable tokens
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- O(1) indexed lookup via HMAC (not O(n) iteration)
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2. **Rate Limiting**
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- Sign-in: 20/3min
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- TOTP verification: 10/3min
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- Token endpoint: 60/min
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- Authorization: 30/min
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- WebAuthn enumeration check: 10/min
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3. **WebAuthn Implementation**
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- Sign count validation (clone detection)
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- Backup eligibility tracking
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- Platform vs roaming authenticator distinction
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- Credential enumeration prevention
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4. **TOTP Implementation**
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- Encrypted secret storage (ActiveRecord Encryption)
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- Backup codes are bcrypt-hashed and single-use
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- Admin can enforce TOTP requirement per user
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5. **Session Security**
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- ACR (Authentication Context Class Reference) tracking
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- `acr: "1"` for password-only, `acr: "2"` for 2FA/passkey
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- Session activity timestamps
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- Remote session revocation
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### Attack Mitigations
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| Attack Vector | Mitigation |
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|---------------|------------|
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| Credential Stuffing | Rate limiting, account lockout via status |
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| Token Theft | HMAC storage, short-lived access tokens, rotation |
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| Session Hijacking | Secure cookies, session binding |
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| CSRF | Rails CSRF protection, state parameter validation |
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| Open Redirect | Strict redirect_uri validation against registered URIs |
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| Authorization Code Injection | PKCE enforcement, redirect_uri binding |
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| Refresh Token Replay | Token rotation, family-based revocation |
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| User Enumeration | Constant-time responses, rate limiting |
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### Areas Reviewed (No Issues Found)
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- Redirect URI validation (exact match required)
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- Client authentication (bcrypt for secrets)
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- Error response handling (no sensitive data leakage in production)
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- Logout implementation (backchannel notifications, session cleanup)
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- Custom claims handling (reserved claim protection)
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---
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## Code Quality Assessment
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### Architecture
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| Aspect | Assessment |
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|--------|------------|
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| Controller Structure | Clean separation, ~900 lines for OIDC (acceptable) |
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| Model Design | Well-normalized, proper associations |
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| Service Objects | Used appropriately (OidcJwtService, ClaimsMerger) |
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| Concerns | TokenPrefixable for shared hashing logic |
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### Code Metrics
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```
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Controllers: ~1,500 lines
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Models: ~1,500 lines
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Services: ~200 lines
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Total App Code: ~3,100 lines
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Test Files: 36 files
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```
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### Readability
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- Clear method naming
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- Inline documentation for complex logic
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- Consistent Ruby style
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- No deeply nested conditionals
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---
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## Test Coverage
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### Test Statistics
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```
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Total Tests: 341
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Assertions: 1,349
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Failures: 0
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Errors: 0
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Run Time: 23.5 seconds (parallel)
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```
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### Test Categories
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| Category | Files | Coverage |
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|----------|-------|----------|
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| OIDC Security | 2 | Auth code reuse, token rotation, PKCE |
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| Integration | 4 | WebAuthn, sessions, invitations, forward auth |
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| Controllers | 8 | All major endpoints |
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| Models | 10 | Validations, associations, business logic |
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| Jobs | 4 | Mailers, token cleanup |
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### Security-Specific Tests
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The test suite includes dedicated security tests:
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- `oidc_authorization_code_security_test.rb` - Code reuse, timing attacks, client auth
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- `oidc_pkce_controller_test.rb` - PKCE flow validation
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- `webauthn_credential_enumeration_test.rb` - Enumeration prevention
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- `session_security_test.rb` - Session handling
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- `totp_security_test.rb` - 2FA bypass prevention
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- `input_validation_test.rb` - Input sanitization
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---
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## Comparison with Reference Implementations
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### vs. Rodauth-OAuth (OpenID Certified)
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| Aspect | Rodauth | Clinch |
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|--------|---------|--------|
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| Modularity | 46 feature modules | Monolithic controller |
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| Token Storage | Optional hashing | HMAC-SHA256 (always) |
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| PKCE | Dedicated feature | Integrated |
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| Certification | OpenID Certified | Not certified |
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Clinch has comparable security but less modularity.
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### vs. Authelia (Production-Grade Go)
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| Aspect | Authelia | Clinch |
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|--------|----------|--------|
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| PKCE Config | `always/public/never` | Per-app toggle |
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| Key Rotation | Supported | Single key |
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| PAR Support | Yes | No |
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| DPoP Support | Yes | No |
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Clinch lacks some advanced features but covers core use cases.
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### vs. Authentik (Enterprise Python)
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| Aspect | Authentik | Clinch |
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|--------|-----------|--------|
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| Scale | Enterprise/distributed | Single instance |
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| Protocols | OAuth, SAML, LDAP, RADIUS | OAuth/OIDC, ForwardAuth |
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| Complexity | High | Low |
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Clinch is intentionally simpler for self-hosting.
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---
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## Recommendations
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### Implemented During Review
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The following issues were identified and fixed during this review:
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1. **Token lookup performance** - Changed from O(n) BCrypt iteration to O(1) HMAC lookup
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2. **`at_hash` claim** - Added per OIDC Core spec
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3. **`auth_time` claim** - Added for authentication timestamp
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4. **`acr` claim** - Added for authentication context class
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5. **`azp` claim** - Added for authorized party
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6. **Authorization code hashing** - Changed from plaintext to HMAC
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7. **Consent SID preservation** - Fixed to preserve pairwise subject ID
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8. **Discovery metadata** - Fixed `subject_types_supported` to `["pairwise"]`
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### Optional Future Enhancements
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| Enhancement | Priority | Effort |
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|-------------|----------|--------|
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| Key Rotation (multi-key JWKS) | Medium | Medium |
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| Token Introspection (RFC 7662) | Low | Low |
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| PAR (RFC 9126) | Low | Medium |
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| OpenID Certification | Low | High |
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---
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## Conclusion
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Clinch provides a solid, security-conscious OIDC/OAuth2 implementation suitable for self-hosted identity management. The codebase demonstrates:
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- **Correct protocol implementation** - Follows OAuth 2.0 and OIDC specifications
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- **Defense in depth** - Multiple layers of security controls
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- **Modern authentication** - WebAuthn/passkeys, TOTP, proper session management
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- **Maintainable code** - Clear structure, good test coverage
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The implementation is appropriate for its intended use case: a lightweight, self-hosted alternative to complex enterprise identity solutions.
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---
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## Methodology
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This review was conducted by examining:
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1. All OIDC-related controllers, models, and services
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2. Reference implementations (Rodauth-OAuth, Authelia, Authentik) in `tmp/`
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3. Test files and coverage
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4. Database schema and migrations
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5. Security-critical code paths
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Tools used: Static analysis, code reading, test execution, comparison with OpenID-certified implementations.
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---
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*This review was conducted by Claude (Anthropic) at the request of the project maintainer. The reviewer has no financial interest in the project.*
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