How I built subdomain-based multi-tenancy with Next.js 14, Supabase RLS, and Cloudflare — for free

Multi-tenancy is one of those things that sounds simple until you're three hours deep into middleware, wildcard DNS, and Row Level Security policies wondering where it all went wrong. I built it for Pronto — an open-source POS, CRM, and booking system for service businesses. Every business that signs up gets their own subdomain: salon-maya.trypronto.app . Fully isolated. One codebase. Here's exactly how I did it, what broke, and what I'd do differently. The architecture in one diagram Client req