ERR-383/stack trace

ERR-383

Cursor app auth not working — fix the 4 most common problems

Cursor app auth not working — fix the 4 most common problems

Last updated 17 April 2026 · 9 min read · By Hyder Shah

Emergency triage — $299 Free diagnostic

Direct answer

Cursor will implement auth flows if you ask — but it implements the happy path. Production auth requires handling: password reset with expiring tokens, session persistence on page reload, OAuth redirect URLs pointing to production not localhost, and RLS policies that actually protect database rows. Four fixes cover 95% of Cursor auth failures.

Quick fix for Cursor app auth not working —

Start here

Fix 1 — Fix OAuth redirect URLs for production

In Supabase Dashboard → Authentication → URL Configuration: add your production URL to Redirect URLs. Format: https://yourapp.com/**.

Common mistake: only localhost:3000is listed. After Vercel deploy, OAuth redirects fail because the callback URL isn’t whitelisted. Add both your production domain and any preview deploy domains.

Deeper fixes when the quick fix fails

Fix 2 — Add onAuthStateChange for session persistence

Add to your auth provider:

useEffect(() => {
  supabase.auth.getSession().then(({ data }) => {
    setSession(data.session);
  });

  const { data: listener } = supabase.auth.onAuthStateChange(
    (_event, session) => setSession(session)
  );

  return () => listener.subscription.unsubscribe();
}, []);

Without both getSession() on mount and the onAuthStateChange listener, refreshing the page logs users out. Cursor frequently forgets one or both.

Fix 3 — Enable and configure Supabase RLS

Auth without RLS means users can read each other’s data even after login. Check each table: Supabase Dashboard → Table Editor → table → RLS. Enable RLS and add policies:

ALTER TABLE your_table ENABLE ROW LEVEL SECURITY;

CREATE POLICY select_own
  ON your_table
  FOR SELECT
  USING (auth.uid() = user_id);

CREATE POLICY insert_own
  ON your_table
  FOR INSERT
  WITH CHECK (auth.uid() = user_id);

CREATE POLICY update_own
  ON your_table
  FOR UPDATE
  USING (auth.uid() = user_id);

CREATE POLICY delete_own
  ON your_table
  FOR DELETE
  USING (auth.uid() = user_id);

Test with two accounts in separate browsers — User A should never see User B’s rows.

04
Fix 4 — Fix password reset for production
In Supabase Dashboard → Authentication → Email Templates → Reset Password: the redirect URL must point to your production site, not localhost.
Update to https://yourapp.com/auth/reset-password. Also check that the reset token expiry (default 24h) matches your UX copy — if your email says “link expires in 1 hour” but Supabase is configured for 24h, users get confused when old links still work.

After the fixes

Test in two incognito windows: sign up as User A, sign up as User B, confirm each sees only their own data. Sign in with OAuth on your production domain, refresh the page, confirm you stay signed in. Request a password reset, confirm the email links to production.

Why AI-built apps hit Cursor app auth not working —

Cursor generates auth code based on your prompt. If you said “add Supabase auth” it added sign-in and sign-up.

It didn’t add: the onAuthStateChange listener that persists sessions across reloads, the production OAuth callback URL, or the database RLS policies that make auth meaningful from a data security perspective.

“Cursor added auth but somehow users can still see each other's data.”

Reddit — r/cursor

Diagnose Cursor app auth not working — by failure mode

Match your symptom to the fix below. Most Cursor auth failures are one of these four.

Symptom	Cause	Fix
OAuth fails in production, works locally	Redirect URL not whitelisted for prod domain	Fix 1
User gets logged out on page refresh	No onAuthStateChange + getSession on mount	Fix 2
Authenticated users can read each other's rows	RLS disabled or missing ownership policies	Fix 3
Password reset email links to localhost	Reset template still using dev URL	Fix 4

Related errors we fix

Still stuck with Cursor app auth not working —?

Emergency triage · $299 · 48h turnaround

We restore service and write the root-cause report.

If any of these apply, an auth audit will save your users’ data and your reputation:

→Users are reporting they can see other users' data
→Login works locally but breaks in production
→Sessions disappear on page refresh
→Password reset emails go to localhost

start the triage →

Free Rescue Diagnostic

30-min call, we tell you what's exposed

Emergency Triage

$299 · 48h

Single auth fix + verification

Security Audit

$499 · 48h

Full auth, RLS, and session audit

Deployment & Launch

From $1,999

Productionization with auth done right

Cursor app auth not working — questions

Why does Cursor auth work locally but fail after deploy?+

Cursor writes auth code that works with the default localhost config. Production adds two breakages: (1) the OAuth redirect URL in Supabase/NextAuth isn't whitelisted for your prod domain, and (2) env vars like NEXT_PUBLIC_SUPABASE_URL may differ between environments. Whitelist the prod domain in the provider dashboard and copy every auth env var into Vercel/Railway.

Why do users get logged out when they refresh a Cursor-built app?+

Cursor often writes sign-in code that sets the session in React state but doesn't restore it on mount. You need both supabase.auth.getSession() on mount (to load the existing session) and supabase.auth.onAuthStateChange() (to react to future logins/logouts). Without both, the session in state disappears on every full-page load.

My Cursor app has auth but users can see each other's data. Why?+

Auth verifies who a user is. RLS (Row Level Security) controls what they can read. Cursor typically adds auth but doesn't enable RLS or add per-user policies, so any authenticated user can run SELECT * on any table. Enable RLS and add `auth.uid() = user_id` policies on every table with user data.

How do I whitelist my production URL in Supabase?+

Supabase Dashboard → Authentication → URL Configuration → Redirect URLs. Add both your production URL (https://yourapp.com/**) and any Vercel preview URLs (https://yourapp-*.vercel.app/**). The ** wildcard is required because OAuth appends query params. Without this, OAuth logins return an error in production.

Why does my password reset email link to localhost?+

Supabase's email templates use whatever redirect URL you last configured. If Cursor set up the reset flow during local dev, the template points to localhost:3000. Go to Authentication → Email Templates → Reset Password and update the redirect URL to your production domain. This applies immediately to new reset emails.

How much does it cost to have you fix Cursor's auth?+

A single auth fix — OAuth URLs, session persistence, or password reset — is $299 as Emergency Triage. A full auth + RLS audit, including all four fixes above plus database-level testing with multiple user accounts, is $499 as a Security Audit. Both include the SQL and code changes committed to your repo.

Next step

Ship the fix. Keep the fix.

Emergency Triage restores service in 48 hours. Break the Fix Loop rebuilds CI so this error cannot ship again.