PostgreSQL Row-Level Security Saved My SaaS From Bugs I Didn't Know I Had

PostgreSQL Row-Level Security Saved My SaaS From Bugs I Didn't Know I Had I build Nokos, an AI note-taking app. Every user's memos, diaries, and coding sessions are stored in one PostgreSQL database. One authorization bug = one user sees another's private data. Most apps have one layer of defense: application-level auth checks. We have two. The second layer — PostgreSQL Row-Level Security — has already caught bugs that our application code missed. The Setup: One Function, Total Isolation Our entire RLS system hinges on one PostgreSQL function: CREATE OR REPLACE FUNCTION current_app_user_id() RETURNS UUID AS $ SELECT NULLIF(current_setting('app.current_user_id', true), '')::UUID; $ LANGUAGE SQL STABLE SECURITY DEFINER; Every table policy checks: WHERE user_id = current_app_user_id(). On every API request, we set the session variable inside a transaction: export async function withRLS<T>( userId: string, callback: (tx: TransactionClient) => Promise<T>, ): Promise<T&gt