Returning a variable to be used within another function

Question

I have generated this code snippet from insomnia that is making a request to an API for an access token. This access token will then be used in another request to retrieve some data via the same API (in the same manner). I want to be able to return the accessToken variable so that when I call the getAccessToken() function it returns the token as a string. My issue is, when I use return accessToken and call the function it comes back as undefined, but when I console log the accessToken (within res.on("end"..)) it prints the token as a string. I have a feeling this is a scope issue but I'm not quite sure how to fix it.

In short, my desired result is to call getAccessToken() and have the function return the access token as a string.

Any help is greatly appreciated!

function getAccessToken() {
  const http = require("https");
  var accessToken;
  const options = {
    "method": "POST",
    "hostname": "omitted for security reasons",
    "port": null,
    "path": "/auth",
    "headers": {
      "Content-Length": "0",
      "Authorization": "Bearer **omitted for security reasons**"
    }
  };

  req = http.request(options, function (res) {
    const chunks = [];

    res.on("data", function (chunk) {
      chunks.push(chunk);
    });

    res.on("end", function () {
      const body = Buffer.concat(chunks);
      accessToken = body.toString();
      return accessToken;
      //console.log(accessToken);
    });
  });

  req.end();
}

console.log(getAccessToken());