Automatically login to moodle when login to another site

I was wondering is it possible to automatically login to moodle after loging-in in aonther site? I tried to use curl but it seems not really working. This is my testing code: //set POST variables $url = "http://moodlesite.com/login/index.php"; $fields = array( 'username' => 'username', 'password' => 'password' ); //open connection $ch = curl_init(); //set the url, number of POST vars, POST data curl_setopt($ch, CURLOPT_URL, $url); curl_setopt($ch, CURLOPT_POST, count($fields)); curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($fields)); curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true); curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE ); curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE ); //execute post $result = curl_exec($ch); //close connection curl_close($ch); I notice that after moodle login to the system, they redirect it again to http://moodlesite.com/login/index.php?testsession=userid and they need cookies it this case.