feat: add multitenant-rbac-tenant-guard sample store - #76

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• ✅ login: li2266 / name: Peng Li (a25ac3e)

Findings

Correct the offboarding claim: removing the direct member tuple does not always revoke access.

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Inline comments:
Review comments at @stores/multitenant-rbac-tenant-guard/store.fga.yaml:
- Around line 26-29: Update the `member` definition in the tenant guard to
accept only direct `user` members, removing `group#member` from the roster so
group membership cannot grant tenant membership.

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Commits

Reviewing files that changed from the base of the PR and between 6802b4d and a25ac3e.

Files selected for processing: 3

• README.md
• stores/multitenant-rbac-tenant-guard/README.md
• stores/multitenant-rbac-tenant-guard/store.fga.yaml

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Walkthrough

This pull request adds a Multi-Tenant RBAC with Tenant Guard OpenFGA store. It defines tenant-scoped authorization, adds fixtures and tests for permission checks and reverse queries, and documents the model.

Changes

Tenant-Guard RBAC

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Feature

Suggested reviewers: aaguiarz

Merge Risk: Low · previous review a25ac

Clarify that offboarding must remove every path to tenant membership; deleting only a direct membership tuple may leave access in place. The documentation correction is bounded and does not block merging.

Pre-merge checks: 5

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title "feat: add multitenant-rbac-tenant-guard sample store" matches the main change. The PR adds a new sample store that demonstrates a tenant-guard pattern for multi-tenant RBAC, with an OpenFGA…
Docstring Coverage		No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Title check

Explanation

The title "feat: add multitenant-rbac-tenant-guard sample store" matches the main change. The PR adds a new sample store that demonstrates a tenant-guard pattern for multi-tenant RBAC, with an OpenFGA model, a test fixture, documentation, and a README table entry. The title is concise, specific, and follows a conventional commit format. It names the store and the feature type, so a teammate scanning history can identify the primary change.

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Hi @li2266

Thanks for the PR!

There's a significant performance trade-off with this approach. Relations with and are significantly more expensive to evaluate. Depending on the hierarchy depth, the impact can be significant.

The tradeoff then is between making sure the relations are properly kept up to date when users are removed from an organization and a runtime performance hit.

Can you please clarify it?

Hi @aaguiarz — thanks for taking the time to review this, and for raising performance; it's exactly the right question for this pattern, and I didn't want to answer it by intuition.

To understand the trade-off I ran both models side by side: OpenFGA v1.22.1 on PostgreSQL 16, caches off, identical fixtures in two stores whose only difference is the five "and member" clauses. The metric is datastore reads per request (Prometheus datastore_query_count deltas), as a proxy for the extra load the guard puts on the database; absolute latencies on a local setup aren't very meaningful, so I only report relative throughput under concurrency.

What I found

Check: the guard adds a constant +2 reads (can_edit) / +5 reads (can_view) at every group depth from 1 to 25. Because the intersection sits on organization capabilities rather than on each resource, it's O(1) per check and doesn't lengthen the serial group chain — the cost is datastore load, not critical-path depth.
ListObjects: flat with document count — 21 vs 20 reads from 100 to 10k documents per tenant, with equal result sets on a clean tenant. With the default weighted-graph pipeline the intersection resolves at the organization node before documents stream; I'd caveat this to v1.22+ with that pipeline enabled.
ListUsers: this is where the cost is real and, I think, unavoidable. Reads stay constant, but the member read returns the whole roster to intersect in memory, so the work grows with roster size — roughly 1.7–2× at 1,000 roster users in my setup.
Concurrency (default pool of 30, all-positive mix): 36 vs 31 reads per check, and roughly 5–20% lower saturated throughput.

The other side of the trade-off

The guard also makes revocation simpler: removing a user's single member tuple cuts off everything in that organization, even if group or role tuples are left behind. I measured that case too — for principals no longer on the roster (offboarded users still in a group, or strangers), the guard short-circuits and the check costs 50–88% fewer reads. In a mixed workload this matters: at 30% negative checks the two models break even on datastore load, and at 50% negatives the guarded store sustains 9–20% higher throughput.

So I'd frame it as a choice for the user rather than a recommendation: a constant per-check cost and a real ListUsers cost on large rosters, in exchange for cross-tenant bindings being inert and offboarding being one tuple. I'd like to add a Trade-offs section to the README with these numbers and an explicit "when to use / when to rely on write-time validation alone" list, and keep the store framed as a defense-in-depth variant alongside multitenant-rbac.

Would it be useful if I also added the benchmark scripts under the store's directory so others can reproduce or extend the measurements? Happy to scope either part down if you'd prefer.