discourse/app/views/users/admin_login.html.erb

<% if @message %>
  <%= @message %>
  <% if @error %><p><%= @error %></p><% end %>
<% else %>
  <%=form_tag(u_admin_login_path, method: :put) do %>
    <%= label_tag(:email, t('admin_login.email_input')) %>
    <%= text_field_tag(:email, nil, autofocus: true) %><br><br>
    <%= submit_tag t('admin_login.submit_button'), class: "btn btn-primary" %>
  <% end %>
<% end %>