layout.phtml

<ul class="nav">
    <li class="active"><a href="/"><?php echo $this->translate('Home') ?></a></li>
    <li>
        <?php $user = $this->session()->offsetGet('user'); ?>
        <?php if ($user): ?>
            <a href="/admin/auth/logout"><?php echo $this->translate('Sair') ?></a>
        <?php else: ?>
            <a href="/admin/auth/index"><?php echo $this->translate('Entrar') ?></a>
        <?php endif;?>

    </li>
</ul>