For one of our social media projects we could use a tool to access an users gMail contacts. We are willing to share this basic class. For advanced usage we suggest using an openauth / openId implementation instead of having an user to POST his google login/password.

/*
 * Copyright (c) 2010 Sam Hermans
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 *
 * gMail Class ...
 * Usage :
 * $gmail = new Gmail('sam.hermans@gmail.com','ThisIsN0tMyPassword');
 * $contacts = $gmail->get_contacts();
 *
 * if($contacts == 1)
 *         die('Login / password field not provided');
 *
 * if($contacts == 2)
 *         die('Login / password incorrect');
 *
 * if(is_array($contacts)) {
 *         $names = array_shift($contacts);
 *         $emails = array_shift($contacts);
 * }
 *
 */

class Gmail {

    private $location = "";
    private $cookiearr = array();
    private $csv_source_encoding='utf-8';
    private $ch;

    private $login;
    private $password;

    public function __construct($login,$password) {
        $this->login = $login;
        $this->password = $password;

    }

    public function get_contacts(){

        #check if username and password was given:
        if ((isset($this->login) && trim($this->login)=="") || (isset($this->password) && trim($this->password)==""))
        {
      #return error code if they weren't
            return 2;
        }

        #initialize the curl session
        $this->ch = curl_init();
        curl_setopt($this->ch, CURLOPT_URL,"https://www.google.com/accounts/ServiceLoginAuth?service=mail");
        curl_setopt($this->ch, CURLOPT_REFERER, "");
        curl_setopt($this->ch, CURLOPT_SSL_VERIFYPEER, 0);
        curl_setopt($this->ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($this->ch, CURLOPT_FOLLOWLOCATION, 1);
        curl_setopt($this->ch, CURLOPT_HEADERFUNCTION, array($this,'read_header'));

        #get the html from gmail.com
        $html = curl_exec($this->ch);

        $matches = array();
        $actionarr = array();

        $action = "https://www.google.com/accounts/ServiceLoginAuth?service=mail";

        #parse the login form:
        #parse all the hidden elements of the form
        preg_match_all('/<input type="hidden"[^>]*name\="([^"]+)"[^>]*value\="([^"]*)"[^>]*>/si', $html, $matches);
        $values = $matches[2];
        $params = "";

        $i=0;
        foreach ($matches[1] as $name)
        {
              $params .= "$name=" . urlencode($values[$i]) . "&";
              ++$i;
        }

        $this->login = urlencode($this->login);
        $this->password = urlencode($this->password);

        #submit the login form:
        curl_setopt($this->ch, CURLOPT_URL,$action);
        curl_setopt($this->ch, CURLOPT_RETURNTRANSFER,1);
        curl_setopt($this->ch, CURLOPT_POST, 1);
        curl_setopt($this->ch, CURLOPT_POSTFIELDS, $params ."Email=$this->login&Passwd=$this->password&PersistentCookie=");

        $html = curl_exec($this->ch);

        #test if login was successful:
        if (!isset($this->cookiearr['GX']) && (!isset($this->cookiearr['LSID']) || $this->cookiearr['LSID'] == "EXPIRED"))
        {
            return 1;
        }

        #this is the new csv url:
        curl_setopt($this->ch, CURLOPT_URL, "http://mail.google.com/mail/contacts/data/export?exportType=ALL&groupToExport=&out=GMAIL_CSV");
        curl_setopt($this->ch, CURLOPT_RETURNTRANSFER,1);
        curl_setopt($this->ch, CURLOPT_HTTPGET, 1);

        $html = curl_exec($this->ch);
        $html = iconv ($this->csv_source_encoding,'utf-8',$html);

        $csvrows = explode("\n", $html);
        array_shift($csvrows);

        $names = array();
        $emails = array();
        foreach ($csvrows as $row)
        {
            if (preg_match('/^((?:"[^"]*")|(?:[^,]*)).*?([^,@]+@[^,]+)/', $row, $matches))
            {
                $names[] = trim( ( trim($matches[1] )=="" ) ? current(explode("@",$matches[2])) : $matches[1] , '" ');
                $emails[] = trim( $matches[2] );
            }
        }

        return array($names, $emails);
    }

    private function read_header($ch,$string) {
        $length = strlen($string);

        if (preg_match("/Content-Type: text\\/csv; charset=([^\s;$]+)/",$string,$matches))
        $this->csv_source_encoding=$matches[1];

        if(!strncmp($string, "Location:", 9))
        {
            $this->location = trim(substr($string, 9, -1));
        }
        if(!strncmp($string, "Set-Cookie:", 11))
        {
            $cookiestr = trim(substr($string, 11, -1));
            $cookie = explode(';', $cookiestr);
            $cookie = explode('=', $cookie[0]);
            $cookiename = trim(array_shift($cookie));
            $this->cookiearr[$cookiename] = trim(implode('=', $cookie));
        }
        $cookie = "";
        if(trim($string) == "")
        {
            foreach ($this->cookiearr as $key=>$value)
            {
                $cookie .= "$key=$value; ";
            }
            curl_setopt($this->ch, CURLOPT_COOKIE, $cookie);
        }

        return $length;
    }

    private function trimvals($val) {
        return trim ($val, "\" \n");
    }

}