client_handle.js

//Below is a JavaScript snippet that parses the response and returns the parameters to the server.

// First, parse the query string
var params = {}, queryString = location.hash.substring(1),
    regex = /([^&=]+)=([^&]*)/g, m;
while (m = regex.exec(queryString)) {
  params[decodeURIComponent(m[1])] = decodeURIComponent(m[2]);
}

// And send the token over to the server
var req = new XMLHttpRequest();
// consider using POST so query isn't logged
req.open('GET', 'https://' + window.location.host + '/catchtoken?' + queryString, true);

req.onreadystatechange = function (e) {
  if (req.readyState == 4) {
     if(req.status == 200){
       window.location = params['state']
   }
  else if(req.status == 400) {
        alert('There was an error processing the token.')
    }
    else {
      alert('something else other than 200 was returned')
    }
  }
};
req.send(null);

//This code sends the parameters received on the fragment to the server using XMLHttpRequest. If your application requires other JavaScript code to make calls to a Google API, you can store the access token in the browser's local storage. Also note that this code sends the parameters to the /catchtoken endpoint, and they are sent over an HTTPS channel.