FastAPI Cookie Not Received by React Frontend: Resolution

When using FastAPI as the backend and React as the frontend communicated via AJAX requests, cookies set by FastAPI might fail to be received by React. This inconsistent behavior can be attributed to the distinct port numbers used by both applications, which creates a cross-origin request scenario.

To address this issue, several steps are necessary:

1. Set Cookies Correctly in FastAPI:
   Ensure that cookies are created and set in FastAPI without errors. Verify that the response includes a 'status': 'success' with a 200 status code.

2. Enable Cookie Acceptance in React:
   Configure the Axios request in your React app to receive cookies by setting the withCredentials property to true. This is necessary for cross-origin requests to include credentials like cookies.

   For example, in Axios:
   await axios.post(url, data, {withCredentials: true}))

   In Fetch API:
   fetch('https://example.com', { credentials: 'include' });

3. Specify Allowed Origins in FastAPI:
   Due to the cross-origin nature of the request, you must explicitly specify the origins allowed to access your API. This includes the domain and port of your React frontend.
4. Allow Credentials in CORSMiddleware:
   In your FastAPI application, ensure that the CORSMiddleware is configured with allow_credentials set to True. This sets the Access-Control-Allow-Credentials header to true, allowing credentials to be included in cross-origin responses.

By following these steps, FastAPI should successfully return cookies to your React frontend. Remember to thoroughly check that the cookie is set correctly, with no errors returned in the Axios POST request.