RFC0055 Identity-Aware Routing

[rkoster]

RFC0055: Identity-Aware mTLS Routing

Implements Phase 1 (1a + 1b) of RFC0055: App-to-App mTLS Routing.

Tracking: cloudfoundry/community#1481
Acceptance Testing Guide: https://gist.github.com/rkoster/5b252b0edca606f10be2dbdcb81a796f

What This Does

Enables GoRouter to enforce mutual TLS and identity-based authorization on a per-domain basis. Apps calling routes on configured mTLS domains must present a valid Diego instance identity certificate. GoRouter extracts the caller's app/space/org identity and checks it against route policies before forwarding the request.

Phase 1a: mTLS Infrastructure

• Per-domain TLS configuration via GetConfigForClient callback (SNI-based)
• Domain-specific client certificate validation against configurable CA
• Domain-aware XFCC header handling with two formats:
  • raw: base64-encoded full certificate (~1.5KB)
  • envoy: compact Hash=...;Subject="..." format (~250 bytes)
• SNI/Host mismatch protection (prevents connection reuse attacks across domains)
• BOSH job properties for router.domains

Phase 1b: Authorization

• Identity extraction from Diego instance identity certificates (Subject DN OUs + SPIFFE URIs)
• Pre-selection auth: validates mTLS domain, client cert presence, identity extraction
• Post-selection auth: enforces route policies (scope and allowed_sources) against selected endpoint
• Supports authorization at app, space, and org granularity
• Default deny when no route policies are configured
• RTR access logs emitted for denied requests (401/403)

Key Design Decisions

• Two-layer authorization: Pre-selection (before endpoint is chosen) handles domain/cert/identity checks. Post-selection (after load balancer picks a backend) handles scope and route-policy checks against the specific endpoint's tags.
• Feature is dormant by default: No behavior change unless router.domains is configured in the BOSH manifest and a shared domain with --enforce-access-rules is created.
• No regression on existing traffic: Non-mTLS domains are completely unaffected.

Testing

• Unit tests for all new handlers and config validation
• Integration tests for end-to-end mTLS routing flows
• BOSH template tests for configuration rendering
• CI runs go fmt, go vet, staticcheck, ginkgo with --race

Configuration Example

# BOSH manifest (via ops-file)
router:
  domains:
    - name: "*.apps.identity"
      ca_certs: "((diego_instance_identity_ca.certificate))"
      forwarded_client_cert: sanitize_set
      xfcc_format: envoy

Related PRs

Component	PR	Status
cloud_controller_ng	cloudfoundry/cloud_controller_ng#4910	Open
capi-release	cloudfoundry/capi-release#625	Open
CLI	cloudfoundry/cli#3758	Draft

Merge Ordering

All PRs are independently safe to merge — the feature is dormant without the ops-file and domain creation. No strict ordering required. Recommend merging around the same time once all are approved.

AI Disclosure

This PR was developed with AI assistance. All code has been read and verified manually. Each error path, branch, and edge case has corresponding test coverage.

[rkoster]

Latest Update: RFC-Compliant Post-Selection Authorization

Implemented breaking change to replace pre-selection authorization with strict post-selection enforcement per RFC lines 475-517.

Key Changes (commit cbf0695)

Architecture:

• ✅ Composable PostSelectionHandler interface for middleware pipeline
• ✅ Separation of pre-selection checks (SNI, route lookup, identity) from post-selection authorization
• ✅ Immediate 403 on authorization failure (non-retriable, per RFC)
• ✅ Post-selection scope checking with :post-selection suffix in metrics

Implementation:

• handlers/post_selection_pipeline.go - Infrastructure for composable checks
• handlers/mtls_scope_auth.go - Org/space boundary enforcement
• handlers/mtls_access_rules_auth.go - Access rules evaluation (cf:app:, cf:space:, etc.)
• handlers/mtls_pre_auth.go - Pre-selection checks only
• handlers/mtls_auth_error.go - Custom error type with Rule/Reason/HTTPStatus

Test Coverage:

• +44 new tests (14 scope + 17 access rules + 13 pipeline)
• +4 integration tests for shared route scenarios
• All 393 tests passing

RFC Compliance

✅ Intermittent 403s - Expected for shared routes across scope boundaries (RFC-compliant)
✅ Error messages - Include "caller org X does not match selected backend org Y"
✅ Strict enforcement - Prevents unauthorized cross-scope access

Breaking Change

⚠️ This replaces the permissive pre-selection authorization entirely. No feature flag provided as this is a security improvement required by the RFC.

Deprecated:

• handlers/mtls_authorization.go (old implementation with migration notes)
• route/pool.go EndpointOrgIDs/SpaceIDs methods

Integration Test Results

All integration tests compile successfully. Shared route scenarios validate:

• Intermittent 403s with scope=space (different spaces in same org)
• Always succeed with scope=org (same org, different spaces)
• Always fail with scope=org (different orgs)
• Per-endpoint access rules with intermittent behavior

Ready for full integration test run and review.

[rkoster]

Refactoring: AuthError for Future Extensibility

Commit: 4ff64b9

Renamed MtlsAuthError to AuthError to prepare for future authentication methods beyond mTLS, such as SPIFFE JWT tokens.

Changes

• ✅ Renamed handlers/mtls_auth_error.go → handlers/auth_error.go
• ✅ Updated struct, constructor functions, and all references
• ✅ Changed error messages from "mTLS authorization denied" to "authorization denied"
• ✅ Updated all test files

Benefits

• 🔮 Future-proof: Ready for SPIFFE JWT token authentication
• 🏗️ Generic design: Error type not tied to specific auth mechanism
• 🧩 Reusable: Can be used across different authentication methods
• ✨ Clean: Better naming convention for authorization errors

No functional changes - pure refactoring for extensibility.