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

<div id='simple-container'>
    <h2><%= t 'activation.welcome_to', site_name: SiteSetting.title %></h2>
    <br/>
    <button class='btn btn-primary' id='activate-account-button'><%= t 'activation.action' %></button>

    <%= form_tag(perform_activate_account_path, method: :put, id: 'activate-account-form') do %>
      <%= hidden_field_tag 'password_confirmation' %>
      <%= hidden_field_tag 'challenge' %>
    <% end %>
</div>

<%- content_for(:no_ember_head) do %>
  <%= preload_script "ember_jquery" %>
  <%= preload_script "vendor" %>
  <%= render_google_universal_analytics_code %>
<%- end %>

<script language="javascript">
  (function() {
    setTimeout(function() {
      var $activateButton = $('#activate-account-button');
      $activateButton.on('click', function() {
        $activateButton.prop('disabled', true);
        $.ajax("<%= path "/u/hp" %>").then(function(hp) {
          $('#password_confirmation').val(hp.value);
          $('#challenge').val(hp.challenge.split("").reverse().join(""));
          $('#activate-account-form').submit();
        }).fail(function() {
          $activateButton.prop('disabled', false);
        });
      });
    }, 50);
  })();
</script>