I'm developing a React application that uses Firebase Authentication for Google sign-in. After successful sign-in, I retrieve the Firebase ID token and send it to my Node.js/Express server for verification.

When I attempt to sign in using Google, I encounter the following errors in my browser's console:

Access to XMLHttpRequest at 'http://localhost:3005/api/verify-token' from origin '' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.


SignUp.jsx:39 Error during sign-in: AxiosError {message: 'Network Error', name: 'AxiosError', code: 'ERR_NETWORK', config: {…}, request: XMLHttpRequest, …}

POST http://localhost:3005/api/verify-token net::ERR_FAILED

My React application is running through ngrok at , and my Express server is running on http://localhost:3005.

My React application is running through ngrok at , and my Express server is running on http://localhost:3005.

What I've Tried:

• I've added the cors middleware to my Express server, specifying the ngrok URL as the allowed origin.

• I've verified that the Firebase Admin SDK is correctly initialized on the server.

• I've made sure that the Authorization header is being sent from the react app.

• I've verified the token verification logic on the server side. My Question:

Why am I still getting the CORS error and the network error? Is there something wrong with my CORS configuration, or is there another issue that I'm overlooking? How do I properly configure my Express server to allow cross-origin requests from my ngrok URL?

Any help would be greatly appreciated.