Why Application-Level Security is Insufficient
In traditional backend architectures, developers rely on Express or Next.js route handlers to verify user permissions before querying the database: if (user.id !== post.author_id) throw Error(). While intuitive, this approach is extremely vulnerable to human error. A single forgot-to-check endpoint or misconfigured GraphQL resolver can expose your entire customer database to public scraping.
PostgreSQL provides an enterprise solution: Row-Level Security (RLS). With RLS, the database engine itself inspects every single SQL query and enforces permission rules directly at the row level, regardless of which client, API route, or background worker submitted the query.
Step 1: Enabling RLS on Every Table
By default, newly created PostgreSQL tables do not enforce row security. You must explicitly activate RLS:
ALTER TABLE public.orders ENABLE ROW LEVEL SECURITY;
ALTER TABLE public.digital_downloads ENABLE ROW LEVEL SECURITY;Step 2: Writing Granular RLS Policies
Policy 1: Public Read Access for Published Content
Allow anyone—including unauthenticated visitors—to read active products, published blog articles, and storefront metadata:
CREATE POLICY "Allow public read access for published products"
ON public.products
FOR SELECT
USING (is_published = true);Policy 2: User-Scoped Order History
Ensure authenticated customers can only query orders matching their unique auth.uid():
CREATE POLICY "Users can only view their own orders"
ON public.orders
FOR SELECT
TO authenticated
USING (auth.uid() = user_id);Policy 3: Administrative Access via Service Role
Allow your automated background workers and administrative scripts to bypass RLS securely using the Supabase Service Role Key:
CREATE POLICY "Service role full access"
ON public.orders
FOR ALL
TO service_role
USING (true)
WITH CHECK (true);Performance Tip: Index Your Security Columns
When RLS is active on high-traffic tables, PostgreSQL must evaluate your policy conditions for every row evaluated. If columns referenced in your USING clauses (such as user_id or is_published) are unindexed, database CPU will spike under load. Always create indexes for RLS query parameters:
CREATE INDEX idx_orders_user_id ON public.orders(user_id);