How to Sync Clerk Users to Supabase with Webhooks (TDD Approach)

The Problem Clerk handles authentication beautifully, but your app logic lives in Supabase. Every time a user signs up or updates their profile, you need a corresponding row in your users table. The solution: a Clerk webhook → /api/webhooks/clerk → upsert into Supabase. Red First: Write Failing Tests // src/lib/__tests__/auth-sync.test.ts describe ( " mapClerkUserToDb " , () => { it ( " maps basic user fields " , () => { const clerkUser = { id : " user_123 " , emailAddresses : [{ emailAddress : " test@example.com " }], firstName : " John " , lastName : " Doe " , }; const result = mapClerkUserToDb ( clerkUser ); expect ( result ). toEqual ({ clerk_id : " user_123 " , email : " test@example.com " , full_name : " John Doe " , plan : " free " , credits : 30 , }); }); }); Tests fail first. That's the point. Green: Implement auth-sync.ts export function mapClerkUserToDb ( clerkUser : ClerkUser ): DbUser { const email = clerkUser . emailAddresses [ 0 ]?. emailAddress ?? "" ; const firstName =