gistfile1.php

<?php
class ExTwitterFormHelper extends TwitterFormHelper {

    /**
     * create OAuth Link
     *
     * @param $options
     *  loading:      loading message
     *  login:        login link text
     *  datasource:   datasource name (default: twitter)
     *  authenticate: use authenticate link (default: false)
     */
    public function oauthLink($options = array()) {

        $default = array(
            'loading' => __d('twitter_kit', 'Loading...', true),
            'login' => __d('twitter_kit', 'Login Twitter', true), 
            'datasource' => 'twitter',
            'authenticate' => false,
            'loginElementId' => 'twitter-login-wrap',
        );

        $options = am($default, $options);

        $action = $options['authenticate'] ? 'authenticate_url' : 'authorize_url';

        $request_url = $this->Html->url(array('plugin' => 'twitter_kit', 'controller' => 'oauth', 'action' => $action . '/' . urlencode($options['datasource'])), true);

        $this->Js->buffer("
            $.getJSON('{$request_url}', {}, function(data){
            var link = $('<a>').attr('href', data.url).html('{$options['login']}');
            $('#{$options['loginElementId']} .loading').remove();
            $('#{$options['loginElementId']}').append(link);
            });
        ");

        $out = sprintf('<span id="%s"><span class="loading">%s</span></span>', $options['loginElementId'], $options['loading']);

        return $this->output($out);
    }

}

gistfile2.php

<?php
$this->ExTwitterForm->oauthLink(array('login' => $this->Html->image('login-button.png')));