How to connect google and allow my user to invite their contacts - php

Question

I have a site, where users sign up. After that they get a great product offer, and I would like to allow them to use from my site "Google connect button" and invite their friends and contacts via Google network.
How can I do that?
Follow up
Sample i found
ex: http://www.dumpsquestions.com/testing/wp-content/themes/ModulaBlueGiant/open/example.php
According to your advise i found that, it allowes a lot ?
Free import contacts (addressbook) script from email providers like
Libero, Interia, Azet, Lycos, AOL, Bordermail, Doramail, Freemail, Kids, Rambler, Mail.ru, Care2, Grafitti, Walla, LinkedIn,
Inbox.com, Mail2World, Meta, IndiaTimes, Sapo.pt, Live/Hotmail, 5Fm, Netaddress, Rediff,
Yahoo!, Aussiemail, KataMail, Gawab, GMX.net, Terra, Uk2, Apropo, Popstarmail, Mynet.com,
YouTube, Bigstring, OperaMail, Mail.com, Mail.in, Nz11, Inet, Pochta, Web.de, Canoe, India, Clevergo, Wp.pt, Evite, Yandex,
GMail, Atlas, Hushmail, O2, Techemail, FastMail, Zapakmail, Virgilio, Abv or social portals like Ning, Hyves, Meinvz, Plurk, Xanga, Tagged, Mydogspace, Konnects, Bebo, Friendfeed, Plazes, Flickr, Cyworld, Last.fm, Mevio, Vkontakte, Skyrock, MySpace, Xuqa, Lovento, Faces, Plaxo, NetLog,
Facebook, Perfspot, Mycatspace, Livejournal, Famiva, Flixster, Xing, Multiply, Brazencareerist, Orkut, Bookcrossing,
Twitter, Koolro, Eons, Hi5, Fdcareer, Motortopia, Vimeo, Kincafe, Flingr, Friendster, Badoo. This contacts importer script is integrating with content management systems (aka CMS) like myBB, Dating Pro, JamRoom, Joomla, PHPMELODY, Boonex Dolphin, Vwebmail, Atmail5, PhpBB, phpFoX, SimpleMachines Forum (SMF), phpizabi, joovili, Joomla1.0, vBulletin, Drupal, jamit job, symfony, Buddy Zone, Wordpress, nowFire, Social Engine, PunBB, RoundCube.
Open Inviter is written in PHP 5 (no database required but cURL or wget required) and running on any webserver (tested on Apache) offering advanced tell a friend features. OpenInviterTM is a free self hosted solution that does not use a third party gateway (or API) to import contacts.
Installation it says:
Openinviter installation Guide.
Thank you for downloading The OpenInviter General Package. This document will guide you through the installation process.
A: Requirements:
Your server will need to have PHP5 installed with DOMDocument support and either cURL or WGET.
B: Install:
1. Extract the contents of the openinviter.tar.gz file you have just downloaded.
Note: tar -xzvf openinviter.tar.gz
2. Upload the extracted files to your webserver (subfolder is highly advised).
3. Run postinstall.php (http://yourdomain/openinviter_dir/postinstall.php)
You may encounter the following errors:
i) The cookie storing folder if not writable. (Change the cookie folder or modify it's permisions.)
ii) Php DOM extension is not installed. (Install dom extension for php)
iii) You don't have curl or wget installed. (Install curl or wget)
You may encounter the following warnings:
i) A plugin does not work properly. (Your server has either a firewall or there is a connectivity error)
Note: You have to fix all the errors or openinviter will probably not work.
Note*: You can't run postinstall.php again for 2 minutes.
4. Edit config.php to suit your needs.
5. Delete postinstall.php
6. Run example.php (http://yourdomain/openinviter_dir/example.php) and try to fetch your contacts.
Note: example.php is modifiable but keep in mind the structure of the file.
Also, its providing a PDF how to do it with PHP, excellent work has been done to respect KISS (keep it simple stupid!!).

Answer 1

Do you want users to be able to login/use your website using their google id? In that case, you can use OpenId, a standardized way to login (you'll be able to use other providers too). For more information about the implementation, look here (http://openid.net/developers/libraries/). This normally done on the server, so probably not with javascript.