Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsA Supabase login that works locally but appears to disappear on Vercel does not point to one confirmed cause. The common split is whether the browser never receives a valid session, or whether the session exists in the browser but your deployed server cannot read, refresh, or safely preserve it. Check the deployed project settings, redirect and PKCE flow, cookie refresh, caching, and authorization checks in that order.
First, determine where the session disappears
Identify your framework, version, authentication method, and whether the affected page is rendered only in the browser or also on the server. A client-only app can read browser local storage; server-rendered code cannot. Supabase’s server-side rendering guide and SSR client guide distinguish these patterns.
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- If login fails before the browser returns to your app, inspect the provider or email redirect and the callback exchange.
- If the browser appears logged in but a server-rendered page treats the request as logged out, check whether the server receives the session in cookies.
- If the session works briefly and then disappears, inspect token refresh, the response that carries refreshed cookies, and caching.
These symptoms narrow the search; without the app’s configuration and request details, none establishes a single cause.
Check that Vercel is using the intended Supabase project
Vercel can assign different environment-variable values to Production, Preview, and Development. Compare the deployed Supabase project URL and public key with the values used locally, and check that the names match the variables your code reads. For a client-side Next.js variable, the name generally needs the NEXT_PUBLIC_ prefix.
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- In Vercel, open the project’s Settings → Environment Variables.
- Check the values and selected environment scopes for the deployment that is failing—Production and Preview are separate cases.
- Confirm that the application’s variable names match those set in Vercel and that the URL and key belong to the intended Supabase project.
- After changing a variable, create a new deployment. Vercel says environment-variable changes do not apply to previous deployments; they apply to new ones. See its Environment Variables documentation.
A mismatch can send the deployed app to a different Supabase project; a missing or stale value can also leave the deployed build misconfigured. These are possibilities to verify, not assumptions about your deployment.
Verify the redirect and the PKCE callback
For OAuth, magic links, signup confirmation, or password recovery, inspect the actual URL reached after the provider or email link redirects. The deployed origin and callback path must be allowed in Supabase’s redirect URL configuration. Also check the configured Site URL if the flow falls back to it: Supabase documents that the default Site URL is localhost:3000 until it is changed. See Password-based Auth.
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With a server-side PKCE flow, the callback needs both the authorization code and the code verifier created when the flow began. Supabase’s PKCE documentation says the code is single-use, valid for five minutes, and must be exchanged in the same browser and device that started the flow. The callback should exchange it with exchangeCodeForSession(code). If the verifier cookie is missing, or the callback response drops its Set-Cookie header, the provider can successfully return to your site while session creation still fails.
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For SSR, make sure the server can receive and refresh the session
Browser local storage is not available to server-rendered pages. In an SSR or hybrid app, use Supabase’s cookie-based server and browser client patterns rather than expecting server code to read a client-only session. Supabase documents this approach in its SSR guide and client creation guide.
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Use the refresh integration for your framework version
For Next.js, Supabase’s current setup uses a Proxy to refresh tokens and make refreshed cookies available to Server Components. In Next.js 16 the file convention is proxy.ts; through Next.js 15 it is middleware.ts. Follow the instructions that match your installed Next.js and @supabase/ssr versions rather than copying an older helper setup. Supabase describes @supabase/ssr as beta and its API as unstable in its SSR documentation.
Return the response that contains the updated cookies
When a token refresh occurs, the response must carry the updated Set-Cookie headers back to the browser. If your handler creates a replacement response or redirects, preserve those cookies and applicable cache headers; otherwise the refresh may happen on the server without persisting in the browser. Supabase explains the cookie propagation requirement in its advanced server-side auth guide.
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Rule out shared caching and cross-request client reuse
An authenticated response can contain a refreshed auth cookie. If a shared cache stores that response and serves it to another user, it can expose or mix user-specific session state. Supabase advises against caching authenticated responses that may carry refreshed cookies. For authenticated Next.js pages, its guidance recommends export const dynamic = 'force-dynamic'; where the framework or library setup does not provide the appropriate headers, use Cache-Control: private, no-store for relevant responses. Preserve cache headers set by the auth integration. Supabase notes that @supabase/ssr v0.10.0 passes cache headers to setAll on refresh. Details are in the advanced guide.
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Use a server-verified identity check for protected data
A session-shaped cookie is not, by itself, proof that a user is authorized. Supabase recommends getClaims() to verify claims when protecting pages or data. Use getUser() when you need a fresh user record confirmed by the Auth server. getSession() can be useful when code needs tokens, but do not rely on its embedded user object for authorization when storage can be influenced by the client. See Supabase’s SSR client guidance.
Match the fix to the app architecture
| App pattern | What the server can read | What to investigate |
|---|---|---|
| Client-only | Browser local storage is available to browser code, not server-rendered code. | Check redirects and browser-side configuration. A server-side missing-session symptom may simply mean the server cannot access the client-only session. |
| SSR or hybrid | Server code needs a session delivered through cookies. | Check framework-specific clients, PKCE callback exchange, refresh integration, cookie propagation, caching, and request isolation. |
For SSR, the exact steps depend on the framework and version, auth method, and whether the failing deployment is a Preview or Production build. Supabase’s current server-side auth guidance describes the supported patterns.
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