.. _wiki2_adding_authorization: ==================== Adding Authorization ==================== :app:`Pyramid` provides facilities for :term:`authentication` and :term:`authorization`. We'll make use of both features to provide security to our application. Our application currently allows anyone with access to the server to view, edit, and add pages to our wiki. We'll change that to allow only people who 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. We will do the following steps: * Add a :term:`root factory` with an :term:`ACL` (``models.py``, ``__init__.py``). * Add an :term:`authentication policy` and an :term:`authorization policy` (``__init__.py``). * Add an authentication policy callback (new ``security.py`` module). * Add routes for /login and /logout (``__init__.py``). * Add ``login`` and ``logout`` views (``views.py``). * Add :term:`permission` declarations to the ``edit_page`` and ``add_page`` views (``views.py``). * Make the existing views return a ``logged_in`` flag to the renderer (``views.py``). * Add a login template (new ``login.pt``). * Add a "Logout" link to be shown when logged in and viewing or editing a page (``view.pt``, ``edit.pt``). The source code for this tutorial stage can be browsed at `http://github.com/Pylons/pyramid/tree/1.3-branch/docs/tutorials/wiki2/src/authorization/ `_. Adding A Root Factory ~~~~~~~~~~~~~~~~~~~~~ Open ``tutorial/tutorial/models.py`` and add the following import statement at the head: .. literalinclude:: src/authorization/tutorial/models.py :lines: 1-4 :linenos: :language: python Add the following class definition: .. literalinclude:: src/authorization/tutorial/models.py :lines: 35-39 :linenos: :language: python The ``RootFactory`` class is a :term:`root factory` that will be used by :app:`Pyramid` to construct the :term:`context` of each request to our application. The context is attached to the request object passed to our view callables as the ``context`` attribute, and will be decorated with security declarations. By using a custom root factory to generate our contexts, we can use the declarative security features of :app:`Pyramid`. Open ``tutorial/tutorial/__init__.py`` and add a ``root_factory`` parameter to our :term:`Configurator` constructor, that points to the class we created above: .. literalinclude:: src/authorization/tutorial/__init__.py :lines: 19-20 :linenos: :emphasize-lines: 2 :language: python (Only the highlighted line needs to be added.) The context object generated by our root factory will possess an ``__acl__`` attribute that allows :data:`pyramid.security.Everyone` (a special principal) to view all pages, while allowing only a :term:`principal` named ``group:editors`` to edit and add pages. The ``__acl__`` attribute attached to a context is interpreted specially by :app:`Pyramid` 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`` argument to :meth:`pyramid.config.Configurator.add_route` for more info. Add an Authorization Policy and an Authentication Policy ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ For any :app:`Pyramid` application to perform authorization, we need to add a ``security.py`` module (we'll do that shortly) and we'll need to change our ``__init__.py`` file to add an :term:`authentication policy` and an :term:`authorization policy` which uses the ``security.py`` file for a *callback*. We'll enable an ``AuthTktAuthenticationPolicy`` and an ``ACLAuthorizationPolicy`` to implement declarative security checking. Open ``tutorial/__init__.py`` and add these import statements: .. literalinclude:: src/authorization/tutorial/__init__.py :lines: 2-3,7 :linenos: :language: python Now add those policies to the configuration: .. literalinclude:: src/authorization/tutorial/__init__.py :lines: 16-22 :linenos: :emphasize-lines: 1-3,6-7 :language: python (Only the highlighted lines need to be added.) Note that the :class:`pyramid.authentication.AuthTktAuthenticationPolicy` constructor accepts two arguments: ``secret`` and ``callback``. ``secret`` is a string representing an encryption key used by the "authentication ticket" machinery represented by this policy: it is required. The ``callback`` is a ``groupfinder`` function in the current directory's ``security.py`` file. We haven't added that module yet, but we're about to. Adding an authentication policy callback ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Create a new ``tutorial/tutorial/security.py`` module with the following content: .. literalinclude:: src/authorization/tutorial/security.py :linenos: :language: python ``groupfinder()`` is an :term:`authentication policy` "callback"; it is a function that accepts a userid and a request and returns one of these values: - 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've given the ``editor`` user membership to the ``group:editors`` by mapping him to this group in the ``GROUPS`` data structure above. Since the ``groupfinder`` function consults the ``GROUPS`` data structure, this will mean that, as a result of the ACL attached to the :term:`context` object returned by the root factory, and the permission associated with the ``add_page`` and ``edit_page`` views, the ``editor`` user should be able to add and edit pages. In a production system, user and group data will most often come from a database, but here we use "dummy" data to represent user and groups sources. Add routes for /login and /logout ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Go back to ``tutorial/tutorial/__init__.py`` and add these two routes: .. literalinclude:: src/authorization/tutorial/__init__.py :lines: 25-26 :linenos: :language: python Adding Login and Logout Views ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ To our ``views.py`` 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. The ``login`` view callable will look something like this: .. literalinclude:: src/authorization/tutorial/views.py :lines: 89-115 :linenos: :language: python The ``logout`` view callable will look something like this: .. literalinclude:: src/authorization/tutorial/views.py :lines: 117-121 :linenos: :language: python The ``login`` view callable is decorated with two decorators, a ``@view_config`` decorator, which associates it with the ``login`` route, and a ``@forbidden_view_config`` decorator which turns it in to an :term:`exception view`. The one which associates it with the ``login`` route makes it visible when we visit ``/login``. The other one makes it a :term:`forbidden view`. The forbidden view is displayed whenever Pyramid or your application raises an :class:`pyramid.httpexceptions.HTTPForbidden` exception. In this case, we'll be relying on the forbidden view to show the login form whenever someone attempts to execute an action which they're not yet authorized to perform. The ``logout`` view callable is decorated with a ``@view_config`` decorator which associates it with the ``logout`` route. This makes it visible when we visit ``/logout``. We'll need to import some stuff to service the needs of these two functions: the ``pyramid.view.forbidden_view_config`` class, a number of values from the ``pyramid.security`` module, and a value from our newly added ``tutorial.security`` package. Add the following import statements to the head of ``tutorial/tutorial/views.py``: .. literalinclude:: src/authorization/tutorial/views.py :lines: 9-18,24-25 :linenos: :emphasize-lines: 3,7-8,12 :language: python (Only the highlighted lines need to be added.) Add permission declarations ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Add a ``permission='edit'`` parameter to the ``@view_config`` decorator for ``add_page()`` and ``edit_page()``, for example: .. code-block:: python :linenos: :emphasize-lines: 2 @view_config(route_name='add_page', renderer='templates/edit.pt', permission='edit') (Only the highlighted line needs to be added.) The result is that only users who possess the ``edit`` permission at the time of the request may invoke those two views. We've granted the ``group:editors`` :term:`principal` the ``edit`` permission in the :term:`root factory` via its ACL, so only a user who is a member of the group named ``group:editors`` will be able to invoke the views associated with the ``add_page`` or ``edit_page`` routes. Return a logged_in flag to the renderer ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Add the following import statement to the head of ``tutorial/tutorial/views.py``: .. code-block:: python :linenos: from pyramid.security import ( authenticated_userid, ) Add a ``logged_in`` parameter to the return value of ``view_page()``, ``edit_page()`` and ``add_page()``, like this: .. code-block:: python :linenos: :emphasize-lines: 3 return dict(page = page, content = content, logged_in = authenticated_userid(request), edit_url = edit_url) (Only the highlighted line needs to be added.) :meth:`~pyramid.security.authenticated_userid()` will return None if the user is not authenticated, or some user id it the user is authenticated. Adding the ``login.pt`` Template ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Create ``tutorial/tutorial/templates/login.pt`` with the following content: .. literalinclude:: src/authorization/tutorial/templates/login.pt :language: xml The above template is referred to within the login view we just added to ``views.py``. Add a "Logout" link when logged in ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Open ``tutorial/tutorial/templates/edit.pt`` and ``tutorial/tutorial/templates/view.pt`` and add this within the ``