.. _wiki2_adding_authorization:

====================
Adding Authorization
====================

Our application currently allows anyone with access to the server to
view, edit, and add pages to our wiki.  For purposes of demonstration
we'll change our application to allow only people whom possess a
specific username (`editor`) to add and edit wiki pages but we'll
continue allowing anyone with access to the server to view pages.
:mod:`repoze.bfg` provides facilities for *authorization* and
*authentication*.  We'll make use of both features to provide security
to our application.

The source code for this tutorial stage can be browsed at
`docs.repoze.org
<http://docs.repoze.org/bfgwiki2-1.2/authorization>`_.

Adding A Root Factory
---------------------

We're going to start to use a custom :term:`root factory` within our
``run.py`` file.  The objects generated by the root factory will be
used as the :term:`context` of each request to our application.  In
order for :mod:`repoze.bfg` declarative security to work properly, the
context object generated during a request must be decorated with
security declarations; when we begin to use a custom root factory to
generate our contexts, we can begin to make use of the declarative
security features of :mod:`repoze.bfg`.

Let's modify our ``run.py``, passing in a :term:`root factory` to our
:term:`Configurator` constructor.  We'll point it at a new class we
create inside our ``models.py`` file.  Add the following statements to
your ``models.py`` file:

.. code-block:: python

   from repoze.bfg.security import Allow
   from repoze.bfg.security import Everyone

   class RootFactory(object):
       __acl__ = [ (Allow, Everyone, 'view'), (Allow, 'editor', 'edit') ]
       def __init__(self, request):
           self.__dict__.update(request.matchdict)

The ``RootFactory`` class we've just added will be used by
:mod:`repoze.bfg` to construct a ``context`` object.  The context is
attached to the request object passed to our view callables as the
``context`` attribute.

All of our context objects will possess an ``__acl__`` attribute that
allows :data:`repoze.bfg.security.Everyone` (a special principal) to
view all pages, while allowing only a user named ``editor`` to edit
and add pages.  The ``__acl__`` attribute attached to a context is
interpreted specially by :mod:`repoze.bfg` as an access control list
during view callable execution.  See :ref:`assigning_acls` for more
information about what an :term:`ACL` represents.

.. note: Although we don't use the functionality here, the ``factory``
   used to create route contexts may differ per-route as opposed to
   globally.  See the ``factory`` attribute in
   :ref:`route_zcml_directive` for more info.

We'll pass the ``RootFactory`` we created in the step above in as the
``root_factory`` argument to a :term:`Configurator`.  When we're done,
your application's ``run.py`` will look like this.

.. literalinclude:: src/authorization/tutorial/run.py
   :linenos:
   :language: python

Configuring a ``repoze.bfg`` Authorization Policy
-------------------------------------------------

For any :mod:`repoze.bfg` application to perform authorization, we
need to add a ``security.py`` module and we'll need to change our
``configure.zcml`` file to add an :term:`authentication policy` and an
:term:`authorization policy`.

Changing ``configure.zcml``
~~~~~~~~~~~~~~~~~~~~~~~~~~~

We'll change our ``configure.zcml`` file to enable an
``AuthTktAuthenticationPolicy`` and an ``ACLAuthorizationPolicy`` to
enable declarative security checking.  We'll also change
``configure.zcml`` to add a ``forbidden`` stanza which points at our
``login`` :term:`view callable`, also known as a :term:`forbidden
view`.  This configures our newly created login view to show up when
:mod:`repoze.bfg` detects that a view invocation can not be
authorized.  Also, we'll add ``view_permission`` attributes with the
value ``edit`` to the ``edit_page`` and ``add_page`` route
declarations.  This indicates that the view callables which these
routes reference cannot be invoked without the authenticated user
possessing the ``edit`` permission with respect to the current
context.  When you're done, your ``configure.zcml`` will look like so

.. literalinclude:: src/authorization/tutorial/configure.zcml
   :linenos:
   :language: xml

Adding ``security.py``
~~~~~~~~~~~~~~~~~~~~~~

Add a ``security.py`` module within your package (in the same
directory as "run.py", "views.py", etc) with the following content:
The groupfinder defined here is an :term:`authentication policy`
"callback"; it is a a callable that accepts a userid and a request.
If the userid exists in the system, the callback will return a
sequence of group identifiers (or an empty sequence if the user isn't
a member of any groups).  If the userid *does not* exist in the
system, the callback will return ``None``.  We'll use "dummy" data to
represent user and groups sources.  When we're done, your
application's ``security.py`` will look like this.

.. literalinclude:: src/authorization/tutorial/security.py
   :linenos:
   :language: python

Adding Login and Logout Views
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We'll add a ``login`` view callable which renders a login form and
processes the post from the login form, checking credentials.

We'll also add a ``logout`` view callable to our application and
provide a link to it.  This view will clear the credentials of the
logged in user and redirect back to the front page.

We'll add a different file (for presentation convenience) to add login
and logout view callables.  Add a file named ``login.py`` to your
application (in the same directory as ``views.py``) with the following
content:

.. literalinclude:: src/authorization/tutorial/login.py
   :linenos:
   :language: python

Changing Existing Views
~~~~~~~~~~~~~~~~~~~~~~~

Then we need to change each of our ``view_page``, ``edit_page`` and
``add_page`` views in ``views.py`` to pass a "logged in" parameter to
its template.  We'll add something like this to each view body:

.. ignore-next-block
.. code-block:: python
   :linenos:

   from repoze.bfg.security import authenticated_userid
   logged_in = authenticated_userid(request)

We'll then change the return value of these views to pass the
`resulting `logged_in`` value to the template, e.g.:

.. ignore-next-block
.. code-block:: python
   :linenos:

   return dict(page = context,
               content = content,
               logged_in = logged_in,
               edit_url = edit_url)

Adding the ``login.pt`` Template
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Add a ``login.pt`` template to your templates directory.  It's
referred to within the login view we just added to ``login.py``.

.. literalinclude:: src/authorization/tutorial/templates/login.pt
   :linenos:
   :language: xml

Change ``view.pt`` and ``edit.pt``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We'll also need to change our ``edit.pt`` and ``view.pt`` templates to
display a "Logout" link if someone is logged in.  This link will
invoke the logout view.

To do so we'll add this to both templates within the ``<div
class="main_content">`` div:

.. code-block:: xml
   :linenos:

   <span tal:condition="logged_in">
      <a href="${request.application_url}/logout">Logout</a>
   </span>

Viewing the Application in a Browser
------------------------------------

We can finally examine our application in a browser.  The views we'll
try are as follows:

- Visiting ``http://localhost:6543/`` in a browser invokes the
  ``view_wiki`` view.  This always redirects to the ``view_page`` view
  of the FrontPage page object.  It is executable by any user.

- Visiting ``http://localhost:6543/FrontPage`` in a browser invokes
  the ``view_page`` view of the FrontPage page object.

- Visiting ``http://localhost:6543/FrontPage/edit_page`` in a browser
  invokes the edit view for the FrontPage object.  It is executable by
  only the ``editor`` user.  If a different user (or the anonymous
  user) invokes it, a login form will be displayed.  Supplying the
  credentials with the username ``editor``, password ``editor`` will
  display the edit page form.

- Visiting ``http://localhost:6543/add_page/SomePageName`` in a
  browser invokes the add view for a page.  It is executable by only
  the ``editor`` user.  If a different user (or the anonymous user)
  invokes it, a login form will be displayed.  Supplying the
  credentials with the username ``editor``, password ``editor`` will
  display the edit page form.

Seeing Our Changes To ``views.py`` and our Templates
----------------------------------------------------

Our ``views.py`` module will look something like this when we're done:

.. literalinclude:: src/authorization/tutorial/views.py
   :linenos:
   :language: python

Our ``edit.pt`` template will look something like this when we're done:

.. literalinclude:: src/authorization/tutorial/templates/edit.pt
   :linenos:
   :language: xml

Our ``view.pt`` template will look something like this when we're done:

.. literalinclude:: src/authorization/tutorial/templates/view.pt
   :linenos:
   :language: xml

Revisiting the Application
---------------------------

When we revisit the application in a browser, and log in (as a result
of hitting an edit or add page and submitting the login form with the
``editor`` credentials), we'll see a Logout link in the upper right
hand corner.  When we click it, we're logged out, and redirected back
to the front page.