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Graph/cors-preflight-cookie-mismatch

Pattern

CORS Preflight Cookie Mismatch

cors-preflight-cookie-mismatch

A recurring cross-site request failure where OPTIONS preflight handling, CORS origin allowlisting, and cookie attributes (SameSite/Secure) disagree, causing 502/blocked cookies between a SPA frontend and an Express backend via a proxy.

Node Details

Public graph metadata

Updated4/30/2026

Connections

30 linked nodes

Axios requests need to work on both client and server in Next.js while switching between DEVICE_TOKEN and AUTH_TOKEN for authentication

502 preflight error between Vue.js frontend and Express backend

Cookie “__vercel_live_token” has been rejected because it is in a cross-site context and its “SameSite” is “Lax” or “Strict” — deployed it on Vercel. Tension: But i setup cookies in my project like this. Outcome: Then you need to use https://localhost:5000 and not http://localhost:5000.

Access to fetch at 'https://askida-backend.vercel.app/payment/create' from origin 'https://www.asunatech.com' has been blocked by CORS policy — from origin 'https://www.asunatech.com'. Tension: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Outcome: How can I properly resolve this CORS issue so that requests from https://www.asunatech.com to my backend are allowed?

When the UI calls the `POST /auth/callback/passkey` endpoint. Tension: Origin servers SHOULD NOT fold multiple Set-Cookie header fields into a single header field. Outcome: Cloudflare seem to be in the wrong here.

Errors from an ASP.NET Core 7 app are not appearing in Sentry, and the console shows `CSRF Verification Failed A required security token was not found or was invalid`.

Sentry reports a CORS error when the Vue 3 app running on http://localhost:3000 tries to send requests to the Sentry DSN, with the browser blocking the fetch due to a missing Access-Control-Allow-Origin header.

requests with the forbidden fields sailed through to the write path. Tension: accepting them would let one client rewrite server-derived state. Outcome: surfacing as a 500 from an unrelated downstream failure in our integration test.

it fails — The code works locally but when I put it on an EC2 machine and change the CORS origins accordingly. Tension: I've checked the URL for 2 hours straight. Outcome: Still the same error below.

Using Fetch from my `index.html` from my `portal.mydomain.com` does not. — Enter `api.mydomain.com` into a browser directly does save my cookie. Tension: I have no CORS errors and the OPTIONS, GET and POST requests all get a 200 response. Outcome: just no cookie, nor can I see the cookie set in my broswer dev tools.

none of customized request headers could be obtained in `UserIdValidationMiddleware` — If the order is reversed, then. Tension: It is not on the axios side. Outcome: Finally, this issue is fixed after reading CORSMiddleware not work and it is related to CORS.

When deployed on Azure App Service behind a proxy, FastAPI/Starlette redirects requests to an HTTP URL (e.g., HTTP Location header in a 307) instead of preserving HTTPS. This causes browser mixed-content/security failures because the app is loaded over HTTPS but redirected to HTTP.

RedirectResponse goes to "/" without the authentication cookie

SessionMiddleware in a FastAPI backend fails to set the session cookie when the React frontend and backend are hosted on different domains/subdomains (e.g., XXX-ui.fly.dev vs XXX-api.fly.dev). The browser rejects the cookie with an 'invalid domain' error and no session is maintained.

were not accessible in js and in browser — Cookies are being set and sent with the next request. Outcome: The problem solved by adding `domain="blueberry.adefe.xyz"` to the cookie in response.

A React frontend POST to http://localhost:4000/api/checkout consistently returns 404 Not Found even though an Express route for checkout is defined.

stripe login returns unexpected http status code: 403

I'm getting CORS error — I'm trying to generate s3 presigned url to upload `video/mp4` files to a bucket from react app client in development mode in my localhost. Tension: the whole thing starts working after a few hours without any changes to the setup. Outcome: the presigned url stops giving cors error.

REST API rejects browser client requests when Content Security Policy is not configured to allow the requesting site

the browser prevents a potential CSRF attack and doesn't include the token — The call is to the backend endpoint specified earlier in `redirect_uri`. Tension: I need a browser to include the `ASP.NET_SessionId` cookie in the request. Outcome: If I set the `SameSite` cookie attribute to `None` the endpoint can be reached.

Browsers started logging a Content Security Policy (CSP) violation indicating that requests to https://vortex.data.microsoft.com/collect/v1 were refused because the page’s connect-src directive does not allow that endpoint.

on Chrome I get an error saying that the CSRF token is mismatched — show a third-party web page (with their approval) in an iframe. Tension: This site has a different domain to my parent site. Outcome: The site displays fine on firefox.

Browser requests to the PHP API from a React/Vite app fail with a CORS error when an Authorization header is included. Requests without custom headers work correctly.

When a REST call returns 403, the React SPA is redirected to the sign-in page, but in development React StrictMode causes the redirect to happen twice (pushing two history entries).

POST requests to the DRF endpoint (/api/posts/) return 401 Unauthorized even though the React Axios request includes a Bearer token in the Authorization header.

Starting the Node/Express server fails with an error: `Route.post() requires a callback function but got a [object Undefined]` originating from `routes/auth.js`.

the first request is always failing since the http-proxy doesn't recognize it as a websocket request. Tension: I struggled to decrypt the accessToken in time and add it to the request before it's sent. Outcome: for now it's not bothering me that much.

Requests to the Django/DRF backend fail with “CSRF Failed: Origin checking failed - http://localhost:8000/ does not match any trusted origins.”

WebSocket connections to `wss://<host>:443` fail when proxied via `tailscale serve` (e.g., port 443 → localhost backend), producing `ERR_SSL_PROTOCOL_ERROR`/TLS internal error and closing immediately. The same backend and proxy config works correctly when served on a custom port (e.g., 8443).

throws "Cookies can only be modified in a Server Action or Route Handler" — called from Next.js 15 Server Components (pages, layouts). Tension: The error appears intermittently — only when the session needs refreshing (controlled by `updateAge` config). Outcome: With `updateAge: 300` (5 minutes), it crashes every ~5 minutes for active users.

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