rollcall-1.php

/**
 * Let Rollcall take care of asking the user for their login and password.
 */

if ($_REQUEST['token'])
  $token = $_REQUEST['token'];
elseif ($_SESSION['token'])
  $token = $_SESSION['token'];
else
  $token = null;

$rollcall_url = 'http://rollcall.aardvark.encorelab.org';
$pest = new PestXML($rollcall_url);

if ($_SESSION['rollcall']) {
  // we're already previously authenticated (see below)
  $rollcall_session = $_SESSION['rollcall'];
} elseif (!$token) {
  $current_url = "http://" . $_SERVER['HTTP_HOST']  . $_SERVER['REQUEST_URI'];

  // redirect to Rollcall for authentication
  header('Location:  '.$rollcall_url.'/login?destination='.$current_url);
  exit();
} else {
  // validate the token
  $rollcall_session = $pest->get('/login/validate_token/'.$token.'.xml')
  // assuming the $token was valid, $session now contains the session
  // data along with the user's account information...
  // you might want to put this under a $_SESSION variable and 
  // check for that next time to avoid re-authenticating on every
  // request.
  $_SESSION['rollcall'] = $rollcall_session;
}

rollcall-2.php

/**
 * You ask the user for login/password yourself. This assumes that
 * your login form was submitted and that the credentials are now under
 * $_REQUEST['login'] and $_REQUEST['password'].
 */

$rollcall_url = 'http://rollcall.aardvark.encorelab.org';
$pest = new PestXML($rollcall_url);

if ($_SESSION['rollcall']) {
  // we're already previously authenticated (see below)
  $rollcall_session = $_SESSION['rollcall'];
} else {
  // validate the token
  $rollcall_session = $pest->post('/login', array(
    'session' => array('login' => $_REQUEST['login'], 'password' => $_REQUEST['password'])
  ))
  // assuming the $credentials were valid, $session now contains the session
  // data along with the user's account information...
  // you might want to put this under a $_SESSION variable and 
  // check for that next time to avoid re-authenticating on every
  // request.
  $_SESSION['rollcall'] = $rollcall_session;
}