After read the docs about links , I’ve changed the template and now no need to pass @conn:
<li><%= link "Logout", to: "/users/logout", method: :delete %></li>
But I still misunderstand why the default template _user_menu.html.eex in mix phx.gen.auth use @conn at: <%= link "Logout", to: Routes.user_session_path(@conn, :delete), method: :delete %>
Btw, I got the worth information at the commit Add security considerations section to docs.
