This function check the google OAuth 2.0 authentification (https://developers.google.com/accounts/docs/OAuth2WebServer), if success login the user or register him.

<#{google_oauth2callback>
  <#{template>
    <script type="text/javascript">
    //<![CDATA[
    <#if condition="<#AMRequest.values['error'] checksum=1>">
      var success = false;
    <#else>
      var success = true;
    <#endif>
 
    (function(){
      if((window.opener !== null) && success){
        window.opener.location = window.opener.location;
      }
      window.close();
    })();
    //]]>
    </script>
  <#}template>    
<#}google_oauth2callback>