config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <Zookal_Customer>
            <version>0.0.1</version>
        </Zookal_Customer>
    </modules>
    <frontend>
        <events>
            <customer_login>
                <observers>
                    <zookalcustomer_customer_login_oauth>
                        <class>zookalcustomer/observer_controller_oAuth</class>
                        <method>saveOAuthRedirectUrl</method>
                    </zookalcustomer_customer_login_oauth>
                </observers>
            </customer_login>
            <controller_action_postdispatch_customer_account_loginPost>
                <observers>
                    <zookalcustomer_customer_apply_oauth_url>
                        <class>zookalcustomer/observer_controller_oAuth</class>
                        <method>applyOAuthRedirectUrl</method>
                    </zookalcustomer_customer_apply_oauth_url>
                </observers>
            </controller_action_postdispatch_customer_account_loginPost>
        </events>
    </frontend>    
</config>

OAuth.php

<?php

class Zookal_Customer_Model_Observer_Controller_OAuth
{

    /**
     * @param string $url
     *
     * @return bool
     */
    protected function _isOAuthUrl($url)
    {
        return strstr(strtolower($url), 'oauth/authorize?oauth_token=') !== FALSE;
    }

    /**
     * Retrieve customer session model object
     *
     * @return Mage_Customer_Model_Session
     */
    protected function _getSession()
    {
        return Mage::getSingleton('customer/session');
    }

    /**
     * @see  http://www.magentocommerce.com/boards/viewthread/438434/
     *
     * @fire customer_login
     */
    public function saveOAuthRedirectUrl()
    {
        $session = $this->_getSession();

        //if this redirect is a result of the OAuth process, force the redirect
        if (TRUE === $this->_isOAuthUrl($session->getBeforeAuthUrl())) {
            $session->setOauthRedirectUrl($session->getBeforeAuthUrl(TRUE));
        }
    }

    /**
     * @fire controller_action_postdispatch_customer_account_loginPost
     *
     * @param Varien_Event_Observer $observer
     */
    public function applyOAuthRedirectUrl(Varien_Event_Observer $observer)
    {
        $session = $this->_getSession();
        /** @var Mage_Customer_AccountController $controller */
        $controller = $observer->getEvent()->getControllerAction();
        if (TRUE === $this->_isOAuthUrl($session->getOauthRedirectUrl())) {
            $controller->getResponse()->setRedirect($session->getOauthRedirectUrl());
        }
    }
}