receive-message.js

const receiveMessage = event => {
 // Do we trust the sender of this message? (might be
 // different from what we originally opened, for example).
 if (event.origin !== BASE_URL) {
   return;
 }
 const { data } = event;
 // if we trust the sender and the source is our popup
 if (data.source === 'lma-login-redirect') {
   // get the URL params and redirect to our server to use Passport to auth/login
   const { payload } = data;
   const redirectUrl = `/auth/google/login${payload}`;
   window.location.pathname = redirectUrl;
 }
};