Supabase Security Expert

Supabase Security Expert (2026 Edition — Auth v3 / PKCE)

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English

Orchestration & Integration

Connects and orchestrates with relevant domain skills like brainstorming, zero-to-prod-orchestrator, and project-context-mapper to ensure cohesive execution.

Description

Expert guide for auditing and hardening Supabase applications. Covers Row Level Security (RLS), Supabase Auth v3 (PKCE flow), API key hygiene, data leakage prevention, Supabase Linter, and production security checklists.

Trigger Conditions

• Auditing RLS policies for correctness and security gaps.
• Setting up Supabase Auth v3 with PKCE flow (replaces implicit flow).
• Reviewing API key usage (anon key vs. service role key).
• Preventing data leakage from misconfigured policies.
• Running Supabase Linter (supabase lint) for automated security checks.
• Implementing user roles and access control in a Supabase project.

Supabase Auth v3 — PKCE Flow (2026 Default)

Supabase Auth v3 now uses PKCE (Proof Key for Code Exchange) as the default flow for all OAuth and magic link authentication — replacing the older implicit flow:

// supabase/client.ts — v3 client setup
import { createBrowserClient } from '@supabase/ssr';

export const supabase = createBrowserClient(
  process.env.NEXT_PUBLIC_SUPABASE_URL!,
  process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!,
  {
    auth: {
      flowType: 'pkce', // Default in Auth v3
      autoRefreshToken: true,
      persistSession: true,
      detectSessionInUrl: true,
    }
  }
);

// Server-side session handling (Next.js App Router)
import { createServerClient } from '@supabase/ssr';
import { cookies } from 'next/headers';

export async function createSupabaseServerClient() {
  const cookieStore = await cookies();
  return createServerClient(
    process.env.NEXT_PUBLIC_SUPABASE_URL!,
    process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!,
    {
      cookies: {
        getAll: () => cookieStore.getAll(),
        setAll: (cookiesToSet) => {
          cookiesToSet.forEach(({ name, value, options }) =>
            cookieStore.set(name, value, options)
          );
        },
      },
    }
  );
}

API Key Security

⚠️ NEVER expose service_role key to the frontend. If it leaks, an attacker can read/write all data in your database, bypassing RLS completely.

// ✅ CORRECT: service_role used only in server-side code
// app/api/admin/route.ts (only accessible at admin.domain.com)
import { createClient } from '@supabase/supabase-js';

const adminClient = createClient(
  process.env.NEXT_PUBLIC_SUPABASE_URL!,
  process.env.SUPABASE_SERVICE_ROLE_KEY!, // NOT exposed to client
);

// 🔴 WRONG: service_role in client-side code
const publicClient = createBrowserClient(url, process.env.SUPABASE_SERVICE_ROLE_KEY!);

RLS Policy Audit Checklist

Common RLS Mistakes

-- 🔴 INSECURE: auth.uid() is not validated — returns null if not authenticated
CREATE POLICY "users can see own data" ON profiles
FOR SELECT USING (user_id = auth.uid());
-- If user is unauthenticated, auth.uid() returns null, which means 
-- NULL = NULL is NULL (falsy in SQL) — so this IS secure... but next one isn't:

-- 🔴 DANGEROUS: Using 'true' without auth check
CREATE POLICY "all can read" ON public_posts
FOR SELECT USING (true);  -- Anyone, including anonymous, can read

-- ✅ SECURE: Explicit authentication requirement
CREATE POLICY "only authenticated users can read" ON sensitive_data
FOR SELECT USING (auth.role() = 'authenticated');

-- ✅ SECURE: Workspace isolation with auth check
CREATE POLICY "workspace isolation" ON projects
FOR ALL USING (
  workspace_id IN (
    SELECT workspace_id FROM workspace_members
    WHERE user_id = auth.uid()
  )
);

RLS Audit SQL Queries

-- Find tables WITHOUT RLS enabled
SELECT schemaname, tablename
FROM pg_tables
WHERE schemaname = 'public'
  AND tablename NOT IN (
    SELECT tablename FROM pg_policies WHERE schemaname = 'public'
  );

-- Find tables with RLS enabled but NO policies (effectively blocks all access)
SELECT c.relname AS table_name, c.relrowsecurity AS rls_enabled
FROM pg_class c
JOIN pg_namespace n ON n.oid = c.relnamespace
WHERE n.nspname = 'public'
  AND c.relkind = 'r'
  AND c.relrowsecurity = true
  AND NOT EXISTS (
    SELECT 1 FROM pg_policies p
    WHERE p.tablename = c.relname AND p.schemaname = n.nspname
  );

Supabase Linter

Run automated security checks:

# Install Supabase CLI
npm install -g supabase

# Run the linter against your project
supabase db lint --project-id <your-project-id>

# Common lint checks:
# - Tables with RLS disabled
# - Policies using mutable functions (NOW(), RANDOM())
# - Security definer functions without search_path
# - Auth functions used incorrectly

Storage Security

// Create a private storage bucket (files not publicly accessible by URL)
const { data, error } = await supabase.storage.createBucket('user-uploads', {
  public: false,  // Private — requires signed URLs
  fileSizeLimit: 10 * 1024 * 1024, // 10MB
  allowedMimeTypes: ['image/jpeg', 'image/png', 'application/pdf'],
});

// Generate a signed URL (expires in 1 hour)
const { data: { signedUrl } } = await supabase.storage
  .from('user-uploads')
  .createSignedUrl(`${userId}/${filename}`, 3600);

-- Storage RLS: users can only access their own files
CREATE POLICY "users can manage own files"
ON storage.objects FOR ALL
USING (bucket_id = 'user-uploads' AND auth.uid()::text = (storage.foldername(name))[1]);

Production Security Checklist

• All tables in public schema have RLS enabled.
• service_role key is only in server-side environment variables.
• PKCE flow enabled (flowType: 'pkce') in Auth v3 client.
• Storage buckets are private by default.
• JWT expiry set appropriately (recommended: 1 hour + refresh tokens).
• Email confirmations required for new signups.
• Supabase Linter (supabase db lint) passes with no critical issues.
• MFA (Multi-Factor Authentication) enabled for admin users.
• Realtime subscriptions restricted — filter by authenticated user.
• Custom auth.uid() policies tested with anonymous/different user sessions.

Bahasa Indonesia

Integrasi Orkestrasi

Terhubung dan mengorkestrasi skill domain yang relevan seperti brainstorming, zero-to-prod-orchestrator, dan project-context-mapper untuk memastikan eksekusi yang kohesif.

Deskripsi

Panduan ahli untuk mengaudit dan mengeraskan aplikasi Supabase. Mencakup Row Level Security (RLS), Supabase Auth v3 (PKCE flow), kebersihan API key, pencegahan kebocoran data, Supabase Linter, dan checklist keamanan produksi.

Kondisi Pemicu

• Mengaudit kebijakan RLS untuk kebenaran dan celah keamanan.
• Menyiapkan Supabase Auth v3 dengan PKCE flow (menggantikan implicit flow).
• Meninjau penggunaan API key (anon key vs. service role key).
• Mencegah kebocoran data dari kebijakan yang salah konfigurasi.
• Menjalankan Supabase Linter untuk pemeriksaan keamanan otomatis.

Supabase Auth v3 — PKCE Flow (Default 2026)

Supabase Auth v3 menggunakan PKCE sebagai alur default untuk semua OAuth dan magic link — menggantikan implicit flow yang lama. Konfigurasikan dengan flowType: 'pkce' di klien browser dan gunakan @supabase/ssr untuk penanganan sesi sisi server di Next.js App Router.

Keamanan API Key

⚠️ JANGAN PERNAH mengekspos service_role key ke frontend. Jika bocor, penyerang dapat membaca/menulis semua data di database Anda, melewati RLS sepenuhnya.

Audit Kebijakan RLS

Kesalahan RLS umum: menggunakan USING (true) tanpa pemeriksaan autentikasi (siapa saja, termasuk anonim, dapat membaca). Selalu verifikasi dengan auth.role() = 'authenticated' atau cek auth.uid() eksplisit.

Gunakan query audit SQL untuk menemukan tabel tanpa RLS dan tabel dengan RLS aktif tetapi tanpa kebijakan (memblokir semua akses).

Supabase Linter

Jalankan supabase db lint untuk pemeriksaan keamanan otomatis: tabel dengan RLS dinonaktifkan, kebijakan menggunakan fungsi yang dapat dimutasi, fungsi security definer tanpa search_path.

Keamanan Storage

Buat bucket penyimpanan privat (public: false) dengan batasan ukuran file dan tipe MIME yang diizinkan. Gunakan URL bertanda tangan (signed URL) untuk memberikan akses sementara ke file privat. Terapkan RLS di storage.objects untuk memastikan pengguna hanya dapat mengakses file mereka sendiri.

Checklist Keamanan Produksi

• Semua tabel di schema public mengaktifkan RLS.
• service_role key hanya di variabel lingkungan sisi server.
• PKCE flow diaktifkan di klien Auth v3.
• Bucket storage privat secara default.
• Supabase Linter tidak ada isu kritis.
• MFA diaktifkan untuk pengguna admin.