title: How to override HTTPForbidden in Ptah?
body: <p>I'm trying out a Pyramid-based web framework, called <em>Ptah</em>, for the first time; I need to override <code>HTTPForbidden</code> view, so that people who are denied access are confronted with a login form. </p>
  
  <pre><code>from pyramid import security
  from pyramid.httpexceptions import HTTPFound, HTTPForbidden
  
  import ptah
  from ptah import form, view
  
  @view.pview(context=HTTPForbidden)
  def login_required(request):
      return str('Hello World')
  </code></pre>
  
  <p>Registering the view this way apparently does not work, but at least the default forbidden view is displayed. How do I override this view?</p>