React Client-side fetched URL doesn't match server-side requested URL - node.js

Question

I'm working on a small nodejs-express-react app. I'm sending a request against the Google Analytics Management API server-side then trying to fetch the response from the client-side. It doesn't work as the Status Code of the fetch is Status Code: 405. however, I'm seeing that the fetched URL is not the same as the requested URL. I don't understand what is wrong exactly.
I'm fetching /auth/google/callback but according to the network information and looking at the error the url requested is https://accounts.google.com/o/oauth2/v2/auth?response_type=code&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2Fauth%2Fgoogle%2Fcallback&client_id=XXXXXXX-XXXXXXX.apps.googleusercontent.com
Here is the full error:
Access to fetch at 'https://accounts.google.com/o/oauth2/v2/auth?response_type=code&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2Fauth%2Fgoogle%2Fcallback&client_id=XXXXXXXX-XXXXXXXX.apps.googleusercontent.com' (redirected from 'http://localhost:5000/auth/google/callback') from origin 'http://localhost:5000' 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. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.
I have this on the server-side:
app.get(
"/auth/google",
passport.authenticate("google", { scope: ['Profile','https://www.googleapis.com/auth/analytics.readonly'] })
);
app.get(
"/auth/google/callback",
passport.authenticate("google", { failureRedirect: "/error", session: false }),
function(req, res) {
var token = req.user.token;
request('https://www.googleapis.com/analytics/v3/management/accounts?access_token=' + token,
function (error, response, body) {
console.log(JSON.parse(body).items);
res.send({data:JSON.parse(body).items})
});
}
);
And this on the client-side:
componentDidMount() {
fetch('/auth/google/callback', {
method: 'GET',
withCredentials: true,
headers: {
'Content-Type': 'application/json',
'Access-Control-Allow-Origin': '*'},
credentials: 'same-origin'
})
.then(res => res.json())
.then(user => this.setState({ data: data }));
}
How should I structure my node/express back-end so I can make the react-side fetch work correctly?
EDIT: I've added 'Access-Control-Allow-Origin': '*' in the header but still got the error.

Answer 1

fetch('/auth/google/callback' requires a full URL (for example https://localhost:8080/auth/google/callback)
EDIT
headers: {
'Content-Type': 'application/json',
'Access-Control-Allow-Origin': '*'
}