Why Isn't My FastAPI Backend Sending Cookies to My React Frontend?

Why FastAPI Is Not Returning Cookies to the React Frontend

When attempting to retrieve cookies from a FastAPI backend within a React frontend, you may find that you're not actually receiving the expected cookies in the response. Several factors contribute to this behavior, such as proper cookie creation, configuration of credential transmission, and correct CORS (Cross-Origin Resource Sharing) setup.

Correctly Setting Cookies

By default, FastAPI does not automatically return cookies in the response. To set a cookie, you must explicitly call the response object's set_cookie() function and specify the key, value, and any additional options (such as max_age or expires). Ensure that there are no errors during the Axios POST request and that you receive a successful response with a status code of 200.

Credential Transmission

In order for your React frontend to receive cookies, you need to enable credential transmission within your Axios requests. By setting the withCredentials property to true, you allow your request to send and receive credentials, such as cookies and authorization headers. This property should be included in every request where you expect to receive credentials from the server.

Additionally, for CORS requests (when your frontend and backend use different domains or ports), the CORS configuration must explicitly allow credential transmission. This can be achieved by setting the allow_credentials option to True in the CORSMiddleware.

CORS Configuration

CORS settings play a crucial role in allowing cross-origin requests and enabling cookie transmission between the frontend and backend. Ensure that your FastAPI application has CORS middleware configured and that the allow_origins list includes the origin of your React frontend.

Proper Axios Configuration

The Axios request should include the withCredentials option set to true:
await axios.post(url, data, { withCredentials: true })

Alternatively, if using Fetch API:
fetch('https://example.com', { credentials: 'include' })

By following these steps, you can successfully set and retrieve cookies between your FastAPI backend and React frontend, allowing for authenticated user handling and access control.

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