Объясните пожалуйста, каким чудом эта страничка производит аутентификацию пользователя. Вида для этого шаблона нет. В шаблоне никаких конструкций типа auth(request.principal) тоже нет. Как?
<html metal:use-macro="context/@@macro_main/master">
<metal:fill fill-slot="body">  
  <div tal:define="principal python:request.principal.id">
    <p tal:condition="python: principal == 'zope.anybody'">
      Please provide Login Information</p>
    <p tal:condition="python: principal != 'zope.anybody'">
      You are not authorized to perform this action. However, you may login
      as a different user who is authorized.</p>
    <form action="" method="post">
      <div tal:omit-tag=""
           tal:condition="python:principal != 'zope.anybody' and 'SUBMIT' in request">
        <span
           tal:define="dummy python:request.response.redirect(request.get('camefrom', ''))" />
      </div>
      <div class="row">
        <div class="label">
          <label for="login">Имя пользователя</label></div>
        <div class="field">
          <input type="text" name="login" id="login" />
        </div>
      </div>

      <div class="row">
        <div class="label">
          <label for="password">Пароль</label></div>
        <div class="field">
          <input type="password" name="password" id="password" />
        </div>
      </div>

      <div class="row">
        <input class="form-element" type="submit"
               name="SUBMIT" value="Log in" />
      </div>
      <input type="hidden" name="camefrom" tal:attributes="value request/camefrom | nothing" />
    </form>
  </div>
</metal:fill>
</html>