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v0 auth breaks in production? How to wire Google OAuth and Supabase without loops

v0 auth breaks in production? How to wire Google OAuth and Supabase without loops

Last updated 15 April 2026 · 9 min read · By Hyder Shah
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Direct answer

v0 Google OAuth breaks the moment you deploy because the redirect URI still points at the preview URL. Fix four surfaces: Google Cloud redirect URIs, Supabase Site URL, cookie domain, and the callback route. 15 minutes end to end. If the loop persists after all four, it’s middleware or a stale session cookie.

Quick fix for v0 auth breaks in production

Start here

Step 1 — Add production URIs to the Google OAuth client

In Google Cloud Console → Credentials → OAuth 2.0 Client, add both the origin (https://yourapp.com) and every callback (https://yourapp.com/auth/callback, https://yourapp.com/api/auth/callback/google) to Authorized redirect URIs. Save. Changes can take a few minutes to propagate.

Deeper fixes when the quick fix fails

  1. 02

    Step 2 — Make sure the callback route exists

    v0 often exports the login button but not the callback. Add app/auth/callback/route.ts (Supabase) or confirm app/api/auth/[...nextauth]/route.ts (NextAuth) made it into the repo. The callback exchanges the code for a session and redirects to the dashboard.

  2. 03

    Step 3 — Fix the cookie domain and middleware

    Session cookies must be set on the production domain, not the preview. If you use middleware (middleware.ts), it must call supabase.auth.getUser() and refresh the session on every request. Check DevTools → Application → Cookies and confirm the cookie domain matches your origin.

  3. 04

    Step 4 — Update Supabase Site URL and Redirect URLs

    In Supabase → Authentication → URL Configuration, set Site URL to https://yourapp.com and add https://yourapp.com/**to Redirect URLs. Remove localhost from production. If you’re using NextAuth instead, set NEXTAUTH_URL to the production origin in Vercel env.

  4. 05

    Step 5 — Redeploy and test in incognito

    Trigger a fresh Vercel deployment so env changes apply. Test in an incognito window — a stale session in your regular browser will lie to you. Watch DevTools → Network for the callback response; it should set a cookie and 302 to your dashboard.

Why AI-built apps hit v0 auth breaks in production

v0 wires OAuth against its preview URL. On deploy, the redirect URI no longer matches the domain the browser is on, so Google rejects the callback, the session never writes, and the app either loops back to /login or lands on a 404.

Supabase (or NextAuth) then compounds the problem: Site URL is still set to the preview, session cookies are set on the wrong domain, and middleware may redirect authenticated users back to /loginbecause it can’t see the session.

“Google OAuth breaks the moment you deploy.”
v0 common failure, 2026

Diagnose v0 auth breaks in production by failure mode

Match the symptom you see to the surface that needs fixing.

SymptomRoot causeFix step
redirect_uri_mismatch from GoogleGoogle Cloud OAuth client missing prod URIStep 1
Callback returns 404App has no /auth/callback route or wrong pathStep 2
Login succeeds, then bounces to /loginSession cookie on wrong domain or middleware blockingStep 3
'Session missing' error in SupabaseSupabase Site URL still points at previewStep 4

Related errors we fix

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  • →Google OAuth loops on every login
  • →Supabase session never persists
  • →Middleware bouncing authenticated users
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v0 auth breaks in production questions

Why does my v0 login work locally but loop on Vercel?+
The redirect URI in Google Cloud still only lists localhost or the v0 preview. Your Vercel origin isn't an approved redirect target, so Google either throws redirect_uri_mismatch or silently fails and the app loops back to /login. Add your production origin and callback to the Google OAuth client, then redeploy.
I added the Vercel URL to Google but login still breaks — why?+
Three other surfaces also need updating. Supabase Site URL, the cookie domain, and any middleware that reads the session all have to point at the production origin. Update all four (Google OAuth, Supabase Site URL, cookie domain, middleware) and test in incognito. A stale session in your current browser will make it look broken even when it is fixed.
What's the difference between Supabase and NextAuth for v0 apps?+
Supabase is auth + database in one, so it wins if you're already using Supabase for data. NextAuth (Auth.js) is auth only and works with any database — better if you're on Neon, PlanetScale, or an existing Postgres. Both have the same production gotcha: the callback URL must match exactly what Google has on file.
Can I fix v0 auth without touching v0?+
Yes. Everything you need to change lives in the exported Next.js repo, in Vercel env, in Supabase (or NextAuth), and in Google Cloud. v0 itself does not need to be touched. Most teams fix production auth entirely outside v0 and never regenerate.
Why do authenticated users get bounced back to /login in production?+
Middleware is reading cookies and not finding a session. Either the callback never wrote the cookie (wrong domain) or middleware isn't refreshing the Supabase session on each request. Use the official Supabase Next.js middleware pattern: create a server client from cookies(), call getUser(), and pass the response back. Details in the Supabase Next.js auth docs.
How much does it cost to have you fix v0 auth?+
Our Integration Fix is $799 fixed for a single integration like auth-done-right (Google OAuth + Supabase session handling + middleware + tested in prod). Emergency Triage for a single blocker is $299 with 48-hour turnaround. A full Deploy-to-Production Pass including auth is $1,999 over 7 days.
Next step

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About the author

Hyder Shah leads Afterbuild Labs, shipping production rescues for apps built in Lovable, Bolt.new, Cursor, Replit, v0, and Base44. our rescue methodology.

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