Example of my App Controller when dealing with shopify in cakephp.php

<?php
/**
 * Application Controller
 * 
 *
 * @package       cake
 * @subpackage    cake.app
 */
class AppController extends Controller {

    var $components = array(
        'Session', 
        'RequestHandler'
    );
    
    var $helpers = array('Session', 'Html', 'Form', 'Js', 'Time');
    
    /**
     * The Shopify API Object
     *
     * @var Object
     */
    var $Shopify = false;


    /**
     * Before Filter. 
     *
     * Sets up any Language Stuff. If you override beforeFilter in your controllers and don't call parent::beforeFilter(), 
     * then don't forget you need to trigger initLanguage() in your beforeFilter
     *
     * This includes initializing the Shopify Session, and checking for validity.
     * If it is invalid, by default we redirect to the Home Page 
     *
     * Otherwise, we make sure we have the token. 
     * If not, we will redirect the user to the Request Permission Url generated by the API. 
     *
     * Lastly, if we've gotten this far, but don't have a Merchant in the session,
     * then we initalize the merchant session.
     *
     * 
     *
     * @return void
     **/
    function beforeFilter() {

        $this->initLanguage();

        $this->initShopifySession();

        //Invalid token for some reason. Trigger an error
        if(!$this->Shopify->valid()) {
            $this->Session->setFlash(__d('errors', 'please_login', true ));
            $this->redirect('/');
            // trigger_error('API Not Valid', E_USER_ERROR);
        }

        //Do we have the token set? If not, redirect to the perm url
        if(!$this->Session->read('Shopify.token')) {
            $this->redirect($this->Shopify->create_permission_url());
        }

        //Everything else has passed, so store the merchant info in the session
        if(!$this->Session->read('Merchant')) {
            $this->initMerchantSession();
        }
        
        if(!$this->Session->read('Shop')) {
            $this->initShopSession();
        }
        
    }


    /**
     * Will initalize any requirements for language. 
     *
     * @return void
     **/
    function initLanguage() {
        Configure::write('Config.language', 'eng');
    }


    /**
     * initShopifySession
     *
     * Check the various $_GET query params to setup $this->Shopify API object
     *
     * Sample URL coming back from Login in via Shopify
     *
     * Set up Shopify session values as well.
     *
     * @return void
     */
    function initShopifySession() {
        
        // We create a Shopify Config which holds our API_KEY and SECRET
        // See shopify.php.default
        Configure::load('shopify');
        
        // Load up the shopify_api. 
        // Unfortunately, it uses some pretty generic class names - in this case, Session.
        App::import('Vendor', 'Session', array('file'=>'shopify_api/lib/shopify_api.php'));
        
        if(isset($_GET['shop'])){
            $this->Session->write('Shopify.shop', $_GET['shop']);
            // We also use this as the Merchant ID - subdomain of myshopify.com
            $this->Session->write('Shopify.shop_id', str_replace('.myshopify.com','', $_GET['shop']));
        }
        
        if(isset($_GET['t'])){
            $this->Session->write('Shopify.token', $_GET['t']);
        }

        $shop = $this->Session->read('Shopify.shop');
        $token = $this->Session->read('Shopify.token');

        $this->Shopify = new Session(
            $shop, 
            $token, 
            Configure::read('Shopify.api_key'), 
            Configure::read('Shopify.secret')
        );
    }


    /**
     * initMerchantSession
     *
     * Initialize the Merchant Session Data.
     * 
     * Looks up the Merchant record, and if it doesn't exist, will create an entry for the Merchant
     *
     * If the Merchant is set to recurring (for billing) then we check with Shopify if it is still active.
     *
     * You would modify this function if there's any additional data you need added to your Merchant session info.
     *
     * @todo Reexamine the use of paid field to do double duty of checking whether merchant is paid/ when they paid. 
     *       See Merchant model for more info 
     * @return void
     **/
    function initMerchantSession() {
        $Merchant = ClassRegistry::init('Merchant');
        $merchantData = $Merchant->read(false, $this->Session->read('Shopify.shop_id'));

        if(!$merchantData) {
            $merchantData = $Merchant->create(array(
                'id'=>$this->Session->read('Shopify.shop_id'),
                'title' => $this->Session->read('Shopify.shop')
            ));

            if(!$Merchant->save()) {
                $this->Session->setFlash(__d('errors','problem_saving_merchant', true));
                $this->redirect('/');
            }
        }

        //If recurring, make sure still valid
        if(1 == $merchantData['Merchant']['recurring']) {
            $chargeInfo = $this->Shopify->recurring_application_charge->get($merchantData['Merchant']['charge_id']);
            if('active' != $chargeInfo['status']) {
                $merchantData['Merchant']['paid'] = null;
            }
        }

        $this->Session->write('Merchant', $merchantData['Merchant']);
    }


    /**
     * Load up the Shop settings.
     * Set whether we are in test more.
     *
     * @return void
     **/
    function initShopSession() {
        $shop = $this->Shopify->shop->get();
        $this->Session->write('Shop',$shop);
        
        //this used in billing. Can check for it for other cases.
        Configure::write('Shopify.test', false);
        if('development' == $shop['plan-name']) {
            Configure::write('Shopify.test', true);
        }
    }


}