How to Correctly Implement Supabase RLS in Next.js App Router Projects

Row Level Security (RLS) is a core Supabase feature that enforces data access control at the database level, but it is frequently misconfigured in Next.js applications. A developer building Wishyze, an AI affirmation platform serving around 28,000 users, documented three common pitfalls encountered while integrating RLS with Next.js 14 and Supabase. The first issue is that RLS is disabled by default on new Supabase tables and must be explicitly enabled via SQL or the dashboard. The second is that the anonymous Supabase key bypasses RLS unless the user is authenticated, and the third involves differences in how server-side and client-side Supabase clients resolve the auth.uid() function used in policies. The article provides code examples for writing correct SELECT, INSERT, and UPDATE policies, and explains how to set up a cookie-aware server client so that RLS policies resolve user identity correctly in App Router API routes.