omnigraph/docs/user/policy.md

Authorization (Cedar policy)

OmniGraph integrates AWS Cedar (cedar-policy = 4.9) for ABAC.

Policy actions

1. read — query / snapshot / list branches & commits
2. export — NDJSON export
3. change — mutations
4. schema_apply — apply schema migrations
5. branch_create
6. branch_delete
7. branch_merge
8. admin — reserved for policy-management surfaces (hot reload, audit log, approvals). No call site today; see MR-724 for the reservation rationale.

Scope kinds

• branch_scope — applied to source branch (read, export, change)
• target_branch_scope — applied to destination (schema_apply, branch ops, run ops)
• protected_branches — named list with special rules; rule scopes are any | protected | unprotected

Configuration

omnigraph.yaml:

policy:
  file: ./policy.yaml          # Cedar rules + groups
  tests: ./policy.tests.yaml   # declarative test cases

Each rule must use exactly one of branch_scope or target_branch_scope.

CLI

• omnigraph policy validate — parse + count actors, exit 1 on parse error.
• omnigraph policy test — run cases in policy.tests.yaml, exit 1 on any expectation mismatch.
• omnigraph policy explain --actor … --action … [--branch …] [--target-branch …] — show decision and matched rule.

Enforcement

Policy is a property of the engine, not the transport. Every mutating write — mutate_as, load_as, ingest_as, apply_schema_as, branch_create_as, branch_create_from_as, branch_delete_as, branch_merge_as — calls Omnigraph::enforce(action, scope, actor) at the head of the method. The gate fires identically whether the call originates from the HTTP server, the CLI, or an embedded SDK consumer. When no PolicyChecker is installed (the dev/embedded default) the gate is a strict no-op; when one is installed and the call site forgets to thread an actor through, the gate fails closed rather than silently bypassing.

Server-side, authorize_request() still runs at the HTTP boundary — that's where actor identity is resolved from the bearer token and where admission control / per-actor rate limits live. Engine-layer enforcement is the defense in depth layer: it catches CLI direct-engine writes, embedded SDK consumers, and any future transport that hasn't (or won't) re-implement HTTP's authorize_request. Both layers consult the same Cedar policy via the same PolicyChecker trait, so decisions cannot disagree.

Coarse vs. fine enforcement

There are two enforcement points, each with non-overlapping responsibilities:

Layer	Question it answers	Where it fires
Engine-layer (coarse)	Can this actor invoke this action against this branch / branch-transition?	Omnigraph::enforce(action, scope, actor) at the head of every _as writer; one Cedar decision per call.
Query-layer (fine)	For the rows / types this action actually touches, which can the actor see or modify?	Per-row predicates pushed into DataFusion at plan time. Not yet implemented — see MR-725.

The engine-layer gate keeps ResourceScope deliberately at branch granularity (Graph, Branch, TargetBranch, BranchTransition). Per-type and per-row authority is the query-layer's job; conflating them in ResourceScope would create two places per-type policy could be evaluated and a drift surface between them.

Actor identity (signed-claim-only)

The actor identity used for every policy decision comes from the matched bearer token — never from a client-supplied request header, query parameter, or body field. The server resolves the token at the auth middleware boundary, looks up the actor it was minted for, and overwrites whatever the handler may have placed in the policy request. Clients cannot set actor_id directly.

This is intentional. Trusting client-supplied identity for authorization is "asking the attacker if they're an admin" — Supabase's RLS history names the same footgun. The chokepoint lives in authorize_request in crates/omnigraph-server/src/lib.rs and is named in docs/dev/invariants.md Hard Invariant 11. A regression test asserts the contract: a request with Authorization: Bearer <token-for-actor-A> plus X-Actor-Id: actor-B always evaluates as actor A, never as actor B.

If you find yourself wanting to let clients override actor_id for impersonation, delegation, or service-account flows — that's a feature, but it needs explicit design (e.g., signed delegation claims, an On-Behalf-Of audit trail). It is not a convenience knob.