how to check user is authenticated in react and express, node using oauth2

I have been looking at the other questions regarding this topic but I cannot seem to figure out the way to do it to achieve my problem.

I have been using Strava api which uses OAuth 2.0. Which follows this process

1. Click connect button
2. Then redirect user to data permissions page
3. after permissions granted then this returns a one time code used to retrieve the access token then the user is redirected to a redirect_uri provided by the developer
4. I redirect the user to another api endpoint of mine which successfully retrieves the access token

Retrieving the access token works I then set the access token as a cookie. This is how I will check user is connected to Strava.

The issue occurs here. I use window.open() to redirect after button click to my backend route which initiates OAuth 2 process. This is where my issue occurs so I want to use context hook in frontend so I tried changing to axios request instead of window.open but I get a cors error due to not having access for Strava cors

Initially I was just checking if res.cookie existed in backend then redirect them to the pages after authenticated but I want to use private routes. Since window.open doesn't return anything I cannot update and check my context to allow user access to private routes.

Does anyone have a better structure or way for me to carry out this process without window.open()

code below:

Home page:

function HomePage() {


   const stravaAuth = async (e) => {


  
  window.open("http://localhost:8800/api/auth/strava/callback", "_self");
  // const res = await axios.get("http://localhost:8800/api/auth/strava/redirect");
  // console.log("res = ", res.data);  
};
  return (
    <div className="App">
      <button onClick={stravaAuth}>Connect to strava!</button>
    </div>
  );
}


export default HomePage;

backend:

let accecssToken;
let athleteID;

async function getDataPromise() {
  const link = `https://www.strava.com/api/v3/activities?access_token=${accecssToken}`;
  console.log("Link = ", link);
  const response = await axios.get(link);
  console.log("Response = ", response.data[0]);
  return response.data;
}

export const stravaActivities = async (req, res) => {
  const data = await getDataPromise();
  console.log("data = ", data);

  return res.json(data);
};

export const stravaCallback = async (req, res) => {
  const client_id = process.env.CLIENT_ID;
  const scope = process.env.SCOPE;
  const redirect_uri = process.env.REDIRECT_URI;
  res.redirect(
    `http://www.strava.com/oauth/authorize?client_id=${client_id}&response_type=code&/exchange_token&approval_prompt=force&scope=${scope}&redirect_uri=${redirect_uri}`
  );

  const accessCode = req.code;
  console.log("One time code = ", accessCode);

  return res.status(200);
};

export const stravaRedirect = async (req, res) => {
  const url = req.url;    
  console.log("url = ", url);
  const accessCode = req.query.code;

  console.log("One time code = ", accessCode);
  const isAuthenticated = false;
  const link = `https://www.strava.com/api/v3/oauth/token?client_id={client_id}&client_secret={client_secret}&code=${accessCode}&grant_type=authorization_code`;
  try {
    const response = await axios.post(link);
    console.log("response = ", JSON.stringify(response.data));
    console.log("access token = ", response.data.access_token);
    accecssToken = response.data.access_token;
    athleteID = response.data.athlete.id;

    res.cookie("Token", accecssToken);
    return res.json(response.data);

  } catch (error) {
    console.log(error);
  }
  res.send(accecssToken);
  // if (res.cookie !== null) {
  //   res.redirect("http://localhost:3000/Activities");
  // } else {
  //   res.redirect("http://localhost:3000");
  // }

};