How to secure a Supabase app built with GitHub Copilot

Where does Copilot read its Supabase MCP config?

• In the IDE: an MCP config such as .vscode/mcp.json, or a server added from an MCP registry.
• In the Copilot CLI: ~/.copilot/mcp-config.json, with OAuth through /mcp.
• Both point at Supabase's hosted server, https://mcp.supabase.com/mcp.

1. Find every place your team configured the Supabase server.
2. Scope each entry to one project and turn on read-only mode, as Supabase's MCP guide describes.
3. Use a development project for daily work. Connect production only when a task needs it.

What access should Copilot's MCP connection have?

Supabase names prompt injection as the main LLM-specific attack on MCP. A General Analysis research demo showed why it matters: an agent in another editor, connected as service_role, followed hidden instructions in a support ticket and copied a private table. No customer breach was reported.

• No service_role or sb_secret_ key in any MCP config file.
• Read-only by default. Writes only for the task that needs them.
• No broad access while Copilot reads text your users submitted.

How do I keep secret keys out of a Copilot-written frontend?

Client code holds the publishable key (sb_publishable_) only. Secret keys and legacy service_role keys stay on servers. Supabase is deprecating the legacy JWT keys by the end of 2026, so this is a good time to move to the new key format.

# Any output means a secret key is in a client variable or in the build.
grep -rlE "(NEXT_PUBLIC_|VITE_|EXPO_PUBLIC_)[A-Z0-9_]*(SECRET|SERVICE)" src/ app/ 2>/dev/null
grep -rlE "sb_secret_|service_role" .next/static/ dist/ build/ 2>/dev/null

How do I ask Copilot for a migration with RLS?

Ask for the table, the RLS statement and the policies together. Name the role and the owner column so Copilot does not fall back to a policy that allows everything.

create table public.messages (
  id bigint generated always as identity primary key,
  sender_id uuid not null references auth.users (id) on delete cascade,
  body text not null,
  created_at timestamptz not null default now()
);
alter table public.messages enable row level security;

create policy "messages: sender reads" on public.messages
  for select to authenticated
  using ((select auth.uid()) = sender_id);

create policy "messages: sender inserts" on public.messages
  for insert to authenticated
  with check ((select auth.uid()) = sender_id);

create index messages_sender_idx on public.messages (sender_id);

How do I check Copilot's policies before they reach production?

1. Run the query below and read every policy that allows all rows. Keep only the ones you meant, such as public read-only content.
2. Run the RLS-off query and expect zero rows.
3. Open Security Advisor and clear lints 0013, 0008, 0010 and 0024.

-- Policies that allow every row.
select tablename, policyname, cmd, roles
from pg_policies
where schemaname = 'public'
  and (qual = 'true' or with_check = 'true');

-- Every table in public without RLS. Expect zero rows.
select c.relname
from pg_class c
join pg_namespace n on n.oid = c.relnamespace
where n.nspname = 'public' and c.relkind = 'r' and not c.relrowsecurity;