This may not help you in this scenario, but I discovered yesterday that you can supply a block to the link helper function. This allows you to provide any HTML within the generated form and link element.
<%= if @current_user do %>
<span class="nav-item">
<%= link to: auth_path(@conn, :delete), method: :delete, class: "button" do %>
Log out
<% end %>
</span>
<% end %>
