Edge functions and webhooks

Secrets and trusted third-party callbacks belong in Supabase Edge Functions (or equivalent server), never in the Vite client bundle.

When to use an edge function

• Webhook signature verification (Stripe, etc.).
• Operations requiring service role or private API keys.
• Sending email with provider API keys.
• Complex server logic that must not be tampered with client-side.

Structure

supabase/functions/
  stripe-webhook/
    index.ts
  send-email/
    index.ts

• Read secrets from Deno.env.get("STRIPE_WEBHOOK_SECRET") etc. — set in Supabase dashboard, not in repo.
• Return proper HTTP status: 400 invalid payload, 401 bad signature, 200 success.
• Make webhook handlers idempotent (store processed event IDs).

Stripe webhook pattern

1. Verify signature with raw body + secret.
2. Switch on event.type; update DB with service client.
3. Respond quickly; heavy work async if needed.

For full Stripe event matrix, idempotency, and testing, use stripe-payment-webhooks, payment-webhook-idempotency, and payment-webhook-testing.

Client invocation

• Use supabase.functions.invoke("send-email", { body: { ... } }) only for operations safe for authenticated users.
• Pass JWT; validate auth.getUser() inside the function for user-triggered calls.

Avoid

• VITE_STRIPE_SECRET_KEY, VITE_SERVICE_ROLE, or webhook secrets in frontend.
• Trusting client-sent payment status without webhook confirmation.
• Logging full webhook payloads with PII in production.

Required companion skills

For any non-trivial edge function, also apply:

• server-input-validation — Zod on every body
• api-error-handling — consistent JSON errors and status codes

Checklist

• CORS configured only if browser calls the function.
• Auth or signature verified on every entry point.
• Body validated with Zod (server-input-validation).
• Errors returned as JSON with stable codes (api-error-handling).
• Secrets via Deno.env.get(...); never logged.