auth

A set of Supabase security guidance for sign-in, permissions, database row security, and separating each customer or workspace's data.

In plain words
What is it for?
Use it when adding authentication, roles, permissions, profiles, workspace context, or multi-tenant data access to a Supabase app.
Why use it?
It helps prevent users from accessing data or actions belonging to another workspace, including when the interface is bypassed.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/tomaspozo/agentlink/auth
Any agent
npx skills add tomaspozo/agentlink --skill auth
Clone the repo
git clone --depth 1 https://github.com/tomaspozo/agentlink

Made for: Claude Code, Codex.

Per session 114 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 7,446 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00114 $0.07446
Opus 5 $0.00057 $0.03723
Sonnet 5 $0.00023 $0.01489
Haiku 4.5 $0.00011 $0.00745

Measured 2d ago against content hash f2ee083f211a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

auth scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/auth/SKILL.md · 437 lines

How it starts

The opening of the file, as written. The whole thing — 437 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Auth, RLS & Multi-Tenancy

Authentication, authorization, and tenant isolation — all enforced by the database.

Security Model — four layers, each with one job

  1. Schema isolation (the table boundary) — Only api.* functions are exposed to clients; public tables are unreachable via the Data API (.from() cannot touch them). This is what actually protects the tables.
  2. RPC permission guard (the permission gate — PRIMARY) — Every mutating api.* RPC calls public.auth_verify_access('<entity>.<action>') as its first statement; it raises HTTP 403 when the caller's active workspace lacks the permission. This is where permission/action authz lives.
  3. RLS, isolation-only (the backstop) — Every table has a cheap policy scoping rows to tenant_id = _auth_tenant_id() and/or user_id = auth.uid(). It is the safety net against a forgotten WHERE — in an agent-built codebase, the worst-case multi-tenant bug. Never put permission checks in RLS — isolation only.
  4. Frontend guard (UX only) — useHasPermission() / route guards hide or redirect. Never security: the backend guard is the real gate; a user who bypasses the UI still hits the 403.

Prerequisite under all of this — GRANTs (explicit, default-deny). api.* RPCs are SECURITY INVOKER, so they touch public tables as the caller, which needs a Postgres table grant just to access the table at all — a separate layer from RLS (grant = "can this role touch the table?"; RLS = "which rows?"). Supabase stopped auto-granting in 2026, and AgentLink keeps default-deny: every table you want reachable needs an explicit GRANT SELECT, INSERT, UPDATE, DELETE … TO authenticated, service_role (bundled with ENABLE ROW LEVEL SECURITY); an ungranted table stays private. anon is never granted on tables (anon-facing RPCs are SECURITY DEFINER). For a read-only table, grant SELECT to authenticated only. Functions are default-deny too, granted per object (no schema-wide GRANT ON ALL FUNCTIONS) — each function REVOKEs the built-in PUBLIC EXECUTE and GRANTs only its roles: api.* client RPCs → authenticated, service_role; api._admin_*service_role; RLS helpers → authenticated. See the database skill's table-privileges rule and the rpc skill's Grants section.

Read the full file on GitHub · 437 lines

Files

What ships with it

2 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 437 lines · 114 tokens per session scan A f2ee083f211a

Subscribe to this mod's changes

auth is a skill published in the GitHub repository tomaspozo/agentlink (6 stars, last pushed 1mo ago), licensed MIT. It adds 114 tokens to every session and 7,446 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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