Supabase JWT in the browser bundle after a Claude Code session

Why Claude Code does this

A CLI agent working across the repo will follow the pattern it already sees. If one component reads a key from `import.meta.env`, the next feature it writes will too — the leak spreads by imitation rather than by a single mistake.

Confirm it first

Before rotating anything, check whether the key is actually being served. Paste your deployed URL — KeyDrift downloads the same JavaScript a visitor gets and tells you what is in it.

Rotate the key

Do this before changing any code. The key has been served to browsers, cached by CDNs and very likely scraped already — removing it from the source does not un-publish it.

1. 1Rotate the key in Project Settings → API. The old one stops working immediately.
2. 2Move whatever needed it into an Edge Function or a server route, and keep only the anon key in the browser.
3. 3Check Row Level Security is enabled on every table — a leaked service_role key bypasses it, so RLS is what limits the damage from the next one.

Move the call to a server

The replacement key must not follow the old one into the bundle, which means the code that uses it cannot live in the browser.

// src/components/Chat.tsx
// Vite substitutes the literal value here at build time.
const key = import.meta.env.VITE_SUPABASE_SERVICE_ROLE_KEY;
const result = await createClient(url, key).from(table).select();

// supabase/functions/admin/index.ts  — runs on a route handler or server action
Deno.serve(async (request) => {
  const key = Deno.env.get('SUPABASE_SERVICE_ROLE_KEY')!; // never sent to the browser
  const result = await createClient(url, key).from(table).select();
  return Response.json(result);
});

// src/components/Chat.tsx
const result = await fetch('/functions/v1/admin', { method: 'POST' }).then((r) => r.json());

How KeyDrift detects it

Matches any three-segment JWT, then decodes the payload — without verifying the signature, because the question is what the token claims to be, not whether it is valid. A `role` claim of `service_role` is critical; `anon` and `authenticated` belong in a browser and are reported as informational. A token issued by `supabase-demo` is the local development default that `supabase start` generates identically on every machine, so it is not treated as a leak.