Something like...
{{ if logged_in }}
{{ if isSuper }}
<li><a href="{{ link to='invoices' }}">Invoices</a></li>
{{ /if }}
<li><a href="{{ link to='users' }}">Users</a></li>
<li><a href="{{ user:logout_url }}">Log out</a></li>
{{ else }}
<li><a href="{{ link to='login' }}">Log in</a></li>
<li><a href="{{ link to='register' }}">Register</a></li>
{{ /if }}