Postman

const authorization = {
  method: 'POST',
  header: {
    Authorization: 'Basic Y2xpZW50OnNlY3JlXX==',
  },
  url: 'http://authserver',
};
pm.sendRequest(authorization, function (err, response) {
  // console.log('authorization');
  // console.log(response.json().access_token);
  // console.log('authorization');
  pm.globals.set('access_token', response.json().access_token);
});

pm.test('Status is ok, respnse is json', () => {
  const access_token = pm.globals.get('access_token');

  pm.response.to.have.status(200);
  pm.response.to.be.ok;
  pm.response.to.json;

  pm.expect(access_token).to.not.be.null;
});