new.html.erb

<h1>Please log in</h1>

<div class='well'>
  <%= form_tag '/login' %>
    <div class='control-group'>
      <%= label_tag :username %>
      <%= text_field_tag :username, params[:username] || '' %>
    </div>

    <div class='control-group'>
      <%= label_tag :password %>
      <%= password_field_tag :password, params[:password] || '' %>
    </div>

    <%= submit_tag "Login", class: 'btn btn-success' %>
  <% end %>
</div>