Postman Pre-request script Cognito Authentication

pm.cogntio.pre-request.js

const echoPostRequest = {
  url: "< auth_url >",
  method: 'POST',
  header: {
    'Accept': 'application/json',
    'Content-Type': 'application/x-www-form-urlencoded',
    'Authorization': "Basic < Base64Encore(client_id:client_secret) >"
  },
  body: {
    mode: 'urlencoded',
    urlencoded: [
      { key: "client_id", value: "< client_id >"},
      { key: "grant_type", value: "client_credentials" },
      { key: "scope", value: "< scope >" }
    ]
  }
};

pm.sendRequest(echoPostRequest, function (err, res) {
  console.log(err ? err : res.json());
  pm.environment.set('Authorization', "Bearer " + res.json().access_token);
});