==================== 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 people who are members of a *group* named ``group:editors`` to add and edit wiki pages but we'll continue allowing anyone with access to the server to view pages. :app:`Pyramid` provides facilities for :term:`authorization` and :term:`authentication`. We'll make use of both features to provide security to our application. We will add an :term:`authentication policy` and an :term:`authorization policy` to our :term:`application registry`, add a ``security.py`` module and give our :term:`root` resource an :term:`ACL`. Then we will add ``login`` and ``logout`` views, and modify the existing views to make them return a ``logged_in`` flag to the renderer and add :term:`permission` declarations to their ``view_config`` decorators. Finally, we will add a ``login.pt`` template and change the existing ``view.pt`` and ``edit.pt`` to show a "Logout" link when not logged in. The source code for this tutorial stage can be browsed via `http://github.com/Pylons/pyramid/tree/1.3-branch/docs/tutorials/wiki/src/authorization/ `_. Add Authentication and Authorization Policies ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We'll change our package's ``__init__.py`` file to enable an ``AuthTktAuthenticationPolicy`` and an ``ACLAuthorizationPolicy`` to enable declarative security checking. We need to import the new policies: .. literalinclude:: src/authorization/tutorial/__init__.py :lines: 4-5,8 :linenos: :language: python Then, we'll add those policies to the configuration: .. literalinclude:: src/authorization/tutorial/__init__.py :lines: 17-22 :linenos: :language: python Note that the creation of an ``AuthTktAuthenticationPolicy`` requires 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 reference to a ``groupfinder`` function in the ``tutorial`` package's ``security.py`` file. We haven't added that module yet, but we're about to. When you're done, your ``__init__.py`` will look like so: .. literalinclude:: src/authorization/tutorial/__init__.py :linenos: :language: python Add ``security.py`` ~~~~~~~~~~~~~~~~~~~ Add a ``security.py`` module within your package (in the same directory as ``__init__.py``, ``views.py``, etc.) with the following content: .. literalinclude:: src/authorization/tutorial/security.py :linenos: :language: python The ``groupfinder`` function defined here is an :term:`authentication policy` "callback"; it is 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``. 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. Note that the ``editor`` user is a member of the ``group:editors`` group in our dummy group data (the ``GROUPS`` data structure). Give Our Root Resource an ACL ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We need to give our root resource object an :term:`ACL`. This ACL will be sufficient to provide enough information to the :app:`Pyramid` security machinery to challenge a user who doesn't have appropriate credentials when he attempts to invoke the ``add_page`` or ``edit_page`` views. We need to perform some imports at module scope in our ``models.py`` file: .. code-block:: python :linenos: from pyramid.security import Allow from pyramid.security import Everyone Our root resource object is a ``Wiki`` instance. We'll add the following line at class scope to our ``Wiki`` class: .. code-block:: python :linenos: __acl__ = [ (Allow, Everyone, 'view'), (Allow, 'group:editors', 'edit') ] It's only happenstance that we're assigning this ACL at class scope. An ACL can be attached to an object *instance* too; this is how "row level security" can be achieved in :app:`Pyramid` applications. We actually only need *one* ACL for the entire system, however, because our security requirements are simple, so this feature is not demonstrated. Our resulting ``models.py`` file will now look like so: .. literalinclude:: src/authorization/tutorial/models.py :linenos: :language: python Add Login and Logout Views ~~~~~~~~~~~~~~~~~~~~~~~~~~ We'll add a ``login`` view which renders a login form and processes the post from the login form, checking credentials. We'll also add a ``logout`` view 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 these views to the existing ``views.py`` file we have in our project. Here's what the ``login`` view callable will look like: .. literalinclude:: src/authorization/tutorial/views.py :lines: 86-113 :linenos: :language: python Here's what the ``logout`` view callable will look like: .. literalinclude:: src/authorization/tutorial/views.py :lines: 115-119 :linenos: :language: python Note that the ``login`` view callable has *two* view configuration decorators. The order of these decorators is unimportant. Each just adds a different :term:`view configuration` for the ``login`` view callable. The first view configuration decorator configures the ``login`` view callable so it will be invoked when someone visits ``/login`` (when the context is a Wiki and the view name is ``login``). The second decorator, named ``forbidden_view_config`` specifies a :term:`forbidden view`. This configures our login view to be presented to the user when :app:`Pyramid` detects that a view invocation can not be authorized. Because we've configured a forbidden view, the ``login`` view callable will be invoked whenever one of our users tries to execute a view callable that they are not allowed to invoke as determined by the :term:`authorization policy` in use. In our application, for example, this means that if a user has not logged in, and he tries to add or edit a Wiki page, he will be shown the login form. Before being allowed to continue on to the add or edit form, he will have to provide credentials that give him permission to add or edit via this login form. Note that we're relying on some additional imports within the bodies of these views (e.g. ``remember`` and ``forget``). We'll see a rendering of the entire views.py file a little later here to show you where those come from. Change Existing Views ~~~~~~~~~~~~~~~~~~~~~ In order to indicate whether the current user is logged in, we need to change each of our ``view_page``, ``edit_page`` and ``add_page`` views in ``views.py`` to pass a "logged in" parameter into its template. We'll add something like this to each view body: .. code-block:: python :linenos: from pyramid.security import authenticated_userid logged_in = authenticated_userid(request) We'll then change the return value of each view that has an associated ``renderer`` to pass the resulting ``logged_in`` value to the template. For example: .. code-block:: python :linenos: return dict(page = context, content = content, logged_in = logged_in, edit_url = edit_url) Add ``permission`` Declarations to our ``view_config`` Decorators ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ To protect each of our views with a particular permission, we need to pass a ``permission`` argument to each of our :class:`pyramid.view.view_config` decorators. To do so, within ``views.py``: - We add ``permission='view'`` to the decorator attached to the ``view_wiki`` and ``view_page`` view functions. This makes the assertion that only users who possess the ``view`` permission against the context resource at the time of the request may invoke these views. We've granted :data:`pyramid.security.Everyone` the view permission at the root model via its ACL, so everyone will be able to invoke the ``view_wiki`` and ``view_page`` views. - We add ``permission='edit'`` to the decorator attached to the ``add_page`` and ``edit_page`` view functions. This makes the assertion that only users who possess the effective ``edit`` permission against the context resource at the time of the request may invoke these views. We've granted the ``group:editors`` principal the ``edit`` permission at the root model via its ACL, so only a user whom is a member of the group named ``group:editors`` will able to invoke the ``add_page`` or ``edit_page`` views. We've likewise given the ``editor`` user membership to this group via the ``security.py`` file by mapping him to the ``group:editors`` group in the ``GROUPS`` data structure (``GROUPS = {'editor':['group:editors']}``); the ``groupfinder`` function consults the ``GROUPS`` data structure. This means that the ``editor`` user can add and edit pages. Add 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 ``views.py``. .. literalinclude:: src/authorization/tutorial/templates/login.pt :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 ``