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 > , ): Pr