{% if user.is_authenticated %}

<form id="logoutForm" action="/logout" method="get" class="form-inline my-2 my-lg-0">
    {% csrf_token %}
    <span class="navbar-brand">Hello {{ user.username }}!</span>
    <a href="javascript:document.getElementById('logoutForm').submit()">Log off</a>
</form>

{% else %}

<ul class="navbar-nav navbar-right">
    <li><a href="{% url 'login' %}">Log in</a></li>
</ul>

{% endif %}