Paypal Login Integration Help

[t194]

I am attempting to implement "Connect with paypal". I have been following this guide. https://developer.paypal.com/docs/connect-with-paypal/

I am looking for some help on what to do after the paypal redirects to my application. 

1. My app loads a popup window via this code provided by paypal https://developer.paypal.com/docs/connect-with-paypal/reference/button-js-builder/
2. A user logs in
3. When successful paypal redirects to a url i provide
4. The url contains the authorisation code authorization_code

What is the best way of  extracting this authorization_code from url, closing the popup window and informing the initial page that opened the popup window that the process has completed.

Are there any events i can listen to?