获取Google API访问令牌

I am writing a JS application to read and write from a Google calendar. I can’t use directly the google api as this is not compatible with my target environment, this is running as a single web page on a local Apache server. For this I am using XmlHttpRequest, this works fine but only when I include an access token ie

   xmlReq.setRequestHeader("Authorization", "Bearer " + GOOGLE_ACCESS_TOKEN);

So what I am trying to do is get the access token using an initial XHR I have been following this doc https://developers.google.com/accounts/docs/OAuth2UserAgent This returns an error with the message :

“No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin localhost is therefore not allowed access.”

I have seen this message already related to XHR cross domain request but I can’t see what is the issue here.

Any ideas ?

Here is the code :

     this.xmlReq = new XMLHttpRequest();
     this.currentUrl='https://accounts.google.com/o/oauth2/auth?'; 
     this.currentUrl += 'response_type=token';
     this.currentUrl += '&redirect_uri=http://localhost';
     this.currentUrl += '&client_id=999999999999.apps.googleusercontent.com';
     this.currentUrl += '&scope=https://www.googleapis.com/auth/calendar';
     this.xmlReq.open("GET", this.currentUrl, true);
     this.xmlReq.responseType = "auth"; 
     this.xmlReq.send();