supabase/supabase

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Core Principles

1. Supabase changes frequently — verify against changelog and current docs before implementing. Do not rely on training data for Supabase features. Function signatures, config.toml settings, and API conventions change between versions.

First, fetch https://supabase.com/changelog.md (a lightweight summary index — not a heavy pull), scan for breaking-change tags relevant to your task, and follow the linked page for any that apply. Then look up the relevant topic using the documentation access methods below.

2. Verify your work. After implementing any fix, run a test query to confirm the change works. A fix without verification is incomplete.

3. Recover from errors, don't loop. If an approach fails after 2-3 attempts, stop and reconsider. Try a different method, check documentation, inspect the error more carefully, and review relevant logs when available. Supabase issues are not always solved by retrying the same command, and the answer is not always in the logs, but logs are often worth checking before proceeding.

4. Exposing tables to the Data API: Depending on the user's Data API settings, newly created tables may not be automatically exposed via the Data (REST) API. If this is the case, anon and authenticated roles will need to be explicitly granted access.

Note that this is separate from RLS, which controls which rows are visible once a table is accessible, not whether the table is accessible at all.

When a user reports a SQL-created table is unexpectedly inaccessible, check their Data API settings and whether the roles have been granted access via explicit GRANT SQL. When granting public (anon/authenticated) access, always enable RLS too. See Exposing a Table to the Data API for the full setup workflow.

5. RLS in exposed schemas. Enable RLS on every table in any exposed schema, which includes public by default. This is critical in Supabase because tables in exposed schemas can be reachable through the Data API when the anon/authenticated roles have access (see Exposing a Table to the Data API). For private schemas, prefer RLS as defense in depth. After enabling RLS, create policies that match the actual access model rather than defaulting every table to the same auth.uid() pattern.

6. Security checklist. When working on any Supabase task that touches auth, RLS, views, storage, or user data, run through this checklist. These are Supabase-specific security traps that silently create vulnerabilities:

• Auth and session security

  • Never use user_metadata claims in JWT-based authorization decisions. In Supabase, raw_user_meta_data is user-editable and can appear in auth.jwt(), so it is unsafe for RLS policies or any other authorization logic. Store authorization data in raw_app_meta_data / app_metadata instead.
  • Deleting a user does not invalidate existing access tokens. Sign out or revoke sessions first, keep JWT expiry short for sensitive apps, and for strict guarantees validate session_id against auth.sessions on sensitive operations.
  • If you use app_metadata or auth.jwt() for authorization, remember JWT claims are not always fresh until the user's token is refreshed.

• API key and client exposure

  • Never expose the service_role or secret key in public clients. Prefer publishable keys for frontend code. Legacy anon keys are only for compatibility. In Next.js, any NEXT_PUBLIC_ env var is sent to the browser.

• RLS, views, and privileged database code

  • Views bypass RLS by default. In Postgres 15 and above, use CREATE VIEW ... WITH (security_invoker = true). In older versions of Postgres, protect your views by revoking access from the anon and authenticated roles, or by putting them in an unexposed schema.
  • UPDATE requires a SELECT policy. In Postgres RLS, an UPDATE needs to first SELECT the row. Without a SELECT policy, updates silently return 0 rows — no error, just no change.
  • auth.role() is deprecated — use the TO clause instead. Supabase has deprecated auth.role() in favour of specifying the target role directly on the policy with TO authenticated or TO anon. Beyond deprecation, auth.role() = 'authenticated' breaks silently when anonymous sign-ins are enabled, because anonymous users carry the authenticated Postgres role and pass the check regardless of whether the user is genuinely signed in.

    -- Deprecated (do not use)
    create policy "example" on table_name for select
    using ( auth.role() = 'authenticated' );
    

  • TO authenticated alone is authentication without authorization (BOLA / IDOR). Using TO authenticated only checks the role — it does not restrict which rows a user can access. The correct pattern combines TO authenticated with an ownership predicate in USING:

    create policy "example" on table_name for select
    to authenticated
    using ( (select auth.uid()) = user_id );
    

  • UPDATE policies require both USING and WITH CHECK. Without WITH CHECK, a user can reassign a row's user_id to another user:

    create policy "example" on table_name for update
    to authenticated
    using ( (select auth.uid()) = user_id )
    with check ( (select auth.uid()) = user_id );
    

  • SECURITY DEFINER functions bypass RLS. A SECURITY DEFINER function runs with its creator's privileges — typically a role with bypassrls (e.g., postgres). Never add SECURITY DEFINER to resolve a permission error; it silently removes access control without fixing the underlying cause. Prefer SECURITY INVOKER.
  • SECURITY DEFINER functions in public are callable by all roles. Postgres grants EXECUTE to PUBLIC by default for every new function, so any SECURITY DEFINER function in public is a public API endpoint callable by anon and authenticated (which inherit from PUBLIC) without any additional grant. When SECURITY DEFINER is genuinely needed (e.g., bypassing RLS on an internal lookup table), keep the function in a non-exposed schema, always include an auth.uid() check in the function body, and run supabase db advisors after making changes.

• Storage access control

  • Storage upsert requires INSERT + SELECT + UPDATE. Granting only INSERT allows new uploads but file replacement (upsert) silently fails. You need all three.

• Dependency and supply-chain security

  • Always pin package versions and commit lockfiles when installing Supabase packages (supabase-js, @supabase/ssr, supabase-py, etc.). See the npm security guide for the full checklist.

For any security concern not covered above, fetch the Supabase product security index: https://supabase.com/docs/guides/security/product-security.md

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