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RAG Thin PEP Around OpenFGA Plan

Goal​

Refactor RAG authorization so the vector service behaves as a policy enforcement point (PEP), not a policy engine. OpenFGA remains the source of truth for datasource and knowledge-base access, while the BFF constrains browser/UI requests before proxying.

Current State​

server/rbac.py currently combines several responsibilities:

  • token validation and role mapping
  • Keycloak realm-role compatibility checks
  • OpenFGA check and list-objects
  • MongoDB team_kb_ownership reads
  • datasource filter injection
  • optional document ACL filtering

That coupling makes query serving depend on multiple policy stores and creates duplicate PDP calls for BFF-proxied UI requests.

Target Call Paths​

CallerExpected RAG behavior
Browser through BFFValidate forwarded JWT, trust BFF-constrained datasource IDs, run vector search.
Direct API userValidate JWT, run one OpenFGA check/list for requested datasource action, run vector search.
Ingestor service accountValidate service token, check service:<id> can_ingest knowledge_base:<id>, run ingest.
Agent/MCP callerValidate JWT, check/constrain datasource access before tool execution.

Migration Slices​

  1. Add explicit tests for UI-proxied search, direct API search, ingestor access, and MCP search.
  2. Extract token parsing from server/rbac.py into a small identity helper.
  3. Extract OpenFGA datasource checks into a small PEP helper with no MongoDB dependency.
  4. Remove team_kb_ownership reads from query hot paths after backfill/drift checks exist.
  5. Keep document ACL as an optional second filter only if it is explicitly enabled and documented.

Non-Goals​

  • Do not remove BFF datasource filtering.
  • Do not remove direct-client RAG OpenFGA checks.
  • Do not use Keycloak realm roles as the long-term source of product authorization.
  • Do not require document reindexing for team membership changes.

Acceptance Checklist​

  • BFF-proxied UI search avoids redundant OpenFGA list/check calls when datasource IDs are already constrained.
  • Direct clients and ingestors still fail closed through explicit OpenFGA checks.
  • MongoDB team_kb_ownership is no longer required in the query hot path.
  • Legacy kb_reader:* / kb_ingestor:* role parsing is removed or isolated as a temporary fallback.
  • Tests cover allowed and denied datasource access for UI, direct API, ingestor, and MCP flows.

Tracked by #1457.