Checking for Facebook Login on Website from Chrome Extension

I want to check from a Chrome extension if I logged in to my website on Google Chrome using the Facebook SDK from javascript and also get the user access token. Right now I am trying to use the following login request on the website:

https://www.facebook.com/v2.12/dialog/oauth?
client_id={app-id}
&redirect_uri={"https://www.example.com/login"}

However, although I am able to call the “https://www.example.com/login” from the chrome extension, I am unable to get the access token for the login. From the chrome extension, how do I determine if somebody has logged into the web app at www.example.com and subsequently get their access token?