.. index:: single: security .. _security_chapter: Security ======== :app:`Pyramid` provides an optional declarative authorization system that can prevent a :term:`view` from being invoked based on an :term:`authorization policy`. Before a view is invoked, the authorization system can use the credentials in the :term:`request` along with the :term:`context` resource to determine if access will be allowed. Here's how it works at a high level: - A :term:`request` is generated when a user visits the application. - Based on the request, a :term:`context` resource is located through :term:`resource location`. A context is located differently depending on whether the application uses :term:`traversal` or :term:`URL dispatch`, but a context is ultimately found in either case. See the :ref:`urldispatch_chapter` chapter for more information. - A :term:`view callable` is located by :term:`view lookup` using the context as well as other attributes of the request. - If an :term:`authentication policy` is in effect, it is passed the request; it returns some number of :term:`principal` identifiers. - If an :term:`authorization policy` is in effect and the :term:`view configuration` associated with the view callable that was found has a :term:`permission` associated with it, the authorization policy is passed the :term:`context`, some number of :term:`principal` identifiers returned by the authentication policy, and the :term:`permission` associated with the view; it will allow or deny access. - If the authorization policy allows access, the view callable is invoked. - If the authorization policy denies access, the view callable is not invoked; instead the :term:`forbidden view` is invoked. Security in :app:`Pyramid`, unlike many systems, cleanly and explicitly separates authentication and authorization. Authentication is merely the mechanism by which credentials provided in the :term:`request` are resolved to one or more :term:`principal` identifiers. These identifiers represent the users and groups in effect during the request. Authorization then determines access based on the :term:`principal` identifiers, the :term:`view callable` being invoked, and the :term:`context` resource. Authorization is enabled by modifying your application to include an :term:`authentication policy` and :term:`authorization policy`. :app:`Pyramid` comes with a variety of implementations of these policies. To provide maximal flexibility, :app:`Pyramid` also allows you to create custom authentication policies and authorization policies. .. index:: single: authorization policy .. _enabling_authorization_policy: Enabling an Authorization Policy -------------------------------- By default, :app:`Pyramid` enables no authorization policy. All views are accessible by completely anonymous users. In order to begin protecting views from execution based on security settings, you need to enable an authorization policy. Enabling an Authorization Policy Imperatively ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Use the :meth:`~pyramid.config.Configurator.set_authorization_policy` method of the :class:`~pyramid.config.Configurator` to enable an authorization policy. You must also enable an :term:`authentication policy` in order to enable the authorization policy. This is because authorization, in general, depends upon authentication. Use the :meth:`~pyramid.config.Configurator.set_authentication_policy` and method during application setup to specify the authentication policy. For example: .. ignore-next-block .. code-block:: python :linenos: from pyramid.config import Configurator from pyramid.authentication import AuthTktAuthenticationPolicy from pyramid.authorization import ACLAuthorizationPolicy authn_policy = AuthTktAuthenticationPolicy('seekrit', hashalg='sha512') authz_policy = ACLAuthorizationPolicy() config = Configurator() config.set_authentication_policy(authn_policy) config.set_authorization_policy(authz_policy) .. note:: the ``authentication_policy`` and ``authorization_policy`` arguments may also be passed to their respective methods mentioned above as :term:`dotted Python name` values, each representing the dotted name path to a suitable implementation global defined at Python module scope. The above configuration enables a policy which compares the value of an "auth ticket" cookie passed in the request's environment which contains a reference to a single :term:`principal` against the principals present in any :term:`ACL` found in the resource tree when attempting to call some :term:`view`. While it is possible to mix and match different authentication and authorization policies, it is an error to configure a Pyramid application with an authentication policy but without the authorization policy or vice versa. If you do this, you'll receive an error at application startup time. See also the :mod:`pyramid.authorization` and :mod:`pyramid.authentication` modules for alternate implementations of authorization and authentication policies. .. index:: single: permissions single: protecting views .. _protecting_views: Protecting Views with Permissions --------------------------------- To protect a :term:`view callable` from invocation based on a user's security settings when a particular type of resource becomes the :term:`context`, you must pass a :term:`permission` to :term:`view configuration`. Permissions are usually just strings, and they have no required composition: you can name permissions whatever you like. For example, the following view declaration protects the view named ``add_entry.html`` when the context resource is of type ``Blog`` with the ``add`` permission using the :meth:`pyramid.config.Configurator.add_view` API: .. code-block:: python :linenos: # config is an instance of pyramid.config.Configurator config.add_view('mypackage.views.blog_entry_add_view', name='add_entry.html', context='mypackage.resources.Blog', permission='add') The equivalent view registration including the ``add`` permission name may be performed via the ``@view_config`` decorator: .. ignore-next-block .. code-block:: python :linenos: from pyramid.view import view_config from resources import Blog @view_config(context=Blog, name='add_entry.html', permission='add') def blog_entry_add_view(request): """ Add blog entry code goes here """ pass As a result of any of these various view configuration statements, if an authorization policy is in place when the view callable is found during normal application operations, the requesting user will need to possess the ``add`` permission against the :term:`context` resource in order to be able to invoke the ``blog_entry_add_view`` view. If he does not, the :term:`Forbidden view` will be invoked. .. index:: pair: permission; default .. _setting_a_default_permission: Setting a Default Permission ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If a permission is not supplied to a view configuration, the registered view will always be executable by entirely anonymous users: any authorization policy in effect is ignored. In support of making it easier to configure applications which are "secure by default", :app:`Pyramid` allows you to configure a *default* permission. If supplied, the default permission is used as the permission string to all view registrations which don't otherwise name a ``permission`` argument. The :meth:`pyramid.config.Configurator.set_default_permission` method supports configuring a default permission for an application. When a default permission is registered: - If a view configuration names an explicit ``permission``, the default permission is ignored for that view registration, and the view-configuration-named permission is used. - If a view configuration names the permission :data:`pyramid.security.NO_PERMISSION_REQUIRED`, the default permission is ignored, and the view is registered *without* a permission (making it available to all callers regardless of their credentials). .. warning:: When you register a default permission, *all* views (even :term:`exception view` views) are protected by a permission. For all views which are truly meant to be anonymously accessible, you will need to associate the view's configuration with the :data:`pyramid.security.NO_PERMISSION_REQUIRED` permission. .. index:: single: ACL single: access control list pair: resource; ACL .. _assigning_acls: Assigning ACLs to your Resource Objects --------------------------------------- When the default :app:`Pyramid` :term:`authorization policy` determines whether a user possesses a particular permission with respect to a resource, it examines the :term:`ACL` associated with the resource. An ACL is associated with a resource by adding an ``__acl__`` attribute to the resource object. This attribute can be defined on the resource *instance* if you need instance-level security, or it can be defined on the resource *class* if you just need type-level security. For example, an ACL might be attached to the resource for a blog via its class: .. code-block:: python :linenos: from pyramid.security import Everyone from pyramid.security import Allow class Blog(object): __acl__ = [ (Allow, Everyone, 'view'), (Allow, 'group:editors', 'add'), (Allow, 'group:editors', 'edit'), ] Or, if your resources are persistent, an ACL might be specified via the ``__acl__`` attribute of an *instance* of a resource: .. code-block:: python :linenos: from pyramid.security import Everyone from pyramid.security import Allow class Blog(object): pass blog = Blog() blog.__acl__ = [ (Allow, Everyone, 'view'), (Allow, 'group:editors', 'add'), (Allow, 'group:editors', 'edit'), ] Whether an ACL is attached to a resource's class or an instance of the resource itself, the effect is the same. It is useful to decorate individual resource instances with an ACL (as opposed to just decorating their class) in applications such as "CMS" systems where fine-grained access is required on an object-by-object basis. .. index:: single: ACE single: access control entry Elements of an ACL ------------------ Here's an example ACL: .. code-block:: python :linenos: from pyramid.security import Everyone from pyramid.security import Allow __acl__ = [ (Allow, Everyone, 'view'), (Allow, 'group:editors', 'add'), (Allow, 'group:editors', 'edit'), ] The example ACL indicates that the :data:`pyramid.security.Everyone` principal -- a special system-defined principal indicating, literally, everyone -- is allowed to view the blog, the ``group:editors`` principal is allowed to add to and edit the blog. Each element of an ACL is an :term:`ACE` or access control entry. For example, in the above code block, there are three ACEs: ``(Allow, Everyone, 'view')``, ``(Allow, 'group:editors', 'add')``, and ``(Allow, 'group:editors', 'edit')``. The first element of any ACE is either :data:`pyramid.security.Allow`, or :data:`pyramid.security.Deny`, representing the action to take when the ACE matches. The second element is a :term:`principal`. The third argument is a permission or sequence of permission names. A principal is usually a user id, however it also may be a group id if your authentication system provides group information and the effective :term:`authentication policy` policy is written to respect group information. For example, the :class:`pyramid.authentication.RepozeWho1AuthenicationPolicy` respects group information if you configure it with a ``callback``. Each ACE in an ACL is processed by an authorization policy *in the order dictated by the ACL*. So if you have an ACL like this: .. code-block:: python :linenos: from pyramid.security import Everyone from pyramid.security import Allow from pyramid.security import Deny __acl__ = [ (Allow, Everyone, 'view'), (Deny, Everyone, 'view'), ] The default authorization policy will *allow* everyone the view permission, even though later in the ACL you have an ACE that denies everyone the view permission. On the other hand, if you have an ACL like this: .. code-block:: python :linenos: from pyramid.security import Everyone from pyramid.security import Allow from pyramid.security import Deny __acl__ = [ (Deny, Everyone, 'view'), (Allow, Everyone, 'view'), ] The authorization policy will deny everyone the view permission, even though later in the ACL is an ACE that allows everyone. The third argument in an ACE can also be a sequence of permission names instead of a single permission name. So instead of creating multiple ACEs representing a number of different permission grants to a single ``group:editors`` group, we can collapse this into a single ACE, as below. .. code-block:: python :linenos: from pyramid.security import Everyone from pyramid.security import Allow __acl__ = [ (Allow, Everyone, 'view'), (Allow, 'group:editors', ('add', 'edit')), ] .. index:: single: principal single: principal names Special Principal Names ----------------------- Special principal names exist in the :mod:`pyramid.security` module. They can be imported for use in your own code to populate ACLs, e.g. :data:`pyramid.security.Everyone`. :data:`pyramid.security.Everyone` Literally, everyone, no matter what. This object is actually a string "under the hood" (``system.Everyone``). Every user "is" the principal named Everyone during every request, even if a security policy is not in use. :data:`pyramid.security.Authenticated` Any user with credentials as determined by the current security policy. You might think of it as any user that is "logged in". This object is actually a string "under the hood" (``system.Authenticated``). .. index:: single: permission names single: special permission names Special Permissions ------------------- Special permission names exist in the :mod:`pyramid.security` module. These can be imported for use in ACLs. .. _all_permissions: :data:`pyramid.security.ALL_PERMISSIONS` An object representing, literally, *all* permissions. Useful in an ACL like so: ``(Allow, 'fred', ALL_PERMISSIONS)``. The ``ALL_PERMISSIONS`` object is actually a stand-in object that has a ``__contains__`` method that always returns ``True``, which, for all known authorization policies, has the effect of indicating that a given principal "has" any permission asked for by the system. .. index:: single: special ACE single: ACE (special) Special ACEs ------------ A convenience :term:`ACE` is defined representing a deny to everyone of all permissions in :data:`pyramid.security.DENY_ALL`. This ACE is often used as the *last* ACE of an ACL to explicitly cause inheriting authorization policies to "stop looking up the traversal tree" (effectively breaking any inheritance). For example, an ACL which allows *only* ``fred`` the view permission for a particular resource despite what inherited ACLs may say when the default authorization policy is in effect might look like so: .. code-block:: python :linenos: from pyramid.security import Allow from pyramid.security import DENY_ALL __acl__ = [ (Allow, 'fred', 'view'), DENY_ALL ] "Under the hood", the :data:`pyramid.security.DENY_ALL` ACE equals the following: .. code-block:: python :linenos: from pyramid.security import ALL_PERMISSIONS __acl__ = [ (Deny, Everyone, ALL_PERMISSIONS) ] .. index:: single: ACL inheritance pair: location-aware; security ACL Inheritance and Location-Awareness -------------------------------------- While the default :term:`authorization policy` is in place, if a resource object does not have an ACL when it is the context, its *parent* is consulted for an ACL. If that object does not have an ACL, *its* parent is consulted for an ACL, ad infinitum, until we've reached the root and there are no more parents left. In order to allow the security machinery to perform ACL inheritance, resource objects must provide *location-awareness*. Providing *location-awareness* means two things: the root object in the resource tree must have a ``__name__`` attribute and a ``__parent__`` attribute. .. code-block:: python :linenos: class Blog(object): __name__ = '' __parent__ = None An object with a ``__parent__`` attribute and a ``__name__`` attribute is said to be *location-aware*. Location-aware objects define an ``__parent__`` attribute which points at their parent object. The root object's ``__parent__`` is ``None``. See :ref:`location_module` for documentations of functions which use location-awareness. See also :ref:`location_aware`. .. index:: single: forbidden view Changing the Forbidden View --------------------------- When :app:`Pyramid` denies a view invocation due to an authorization denial, the special ``forbidden`` view is invoked. "Out of the box", this forbidden view is very plain. See :ref:`changing_the_forbidden_view` within :ref:`hooks_chapter` for instructions on how to create a custom forbidden view and arrange for it to be called when view authorization is denied. .. index:: single: debugging authorization failures .. _debug_authorization_section: Debugging View Authorization Failures ------------------------------------- If your application in your judgment is allowing or denying view access inappropriately, start your application under a shell using the ``PYRAMID_DEBUG_AUTHORIZATION`` environment variable set to ``1``. For example: .. code-block:: text $ PYRAMID_DEBUG_AUTHORIZATION=1 bin/pserve myproject.ini When any authorization takes place during a top-level view rendering, a message will be logged to the console (to stderr) about what ACE in which ACL permitted or denied the authorization based on authentication information. This behavior can also be turned on in the application ``.ini`` file by setting the ``pyramid.debug_authorization`` key to ``true`` within the application's configuration section, e.g.: .. code-block:: ini :linenos: [app:main] use = egg:MyProject pyramid.debug_authorization = true With this debug flag turned on, the response sent to the browser will also contain security debugging information in its body. Debugging Imperative Authorization Failures ------------------------------------------- The :func:`pyramid.security.has_permission` API is used to check security within view functions imperatively. It returns instances of objects that are effectively booleans. But these objects are not raw ``True`` or ``False`` objects, and have information attached to them about why the permission was allowed or denied. The object will be one of :data:`pyramid.security.ACLAllowed`, :data:`pyramid.security.ACLDenied`, :data:`pyramid.security.Allowed`, or :data:`pyramid.security.Denied`, as documented in :ref:`security_module`. At the very minimum these objects will have a ``msg`` attribute, which is a string indicating why the permission was denied or allowed. Introspecting this information in the debugger or via print statements when a call to :func:`~pyramid.security.has_permission` fails is often useful. .. index:: single: authentication policy (creating) .. _creating_an_authentication_policy: Creating Your Own Authentication Policy --------------------------------------- :app:`Pyramid` ships with a number of useful out-of-the-box security policies (see :mod:`pyramid.authentication`). However, creating your own authentication policy is often necessary when you want to control the "horizontal and vertical" of how your users authenticate. Doing so is a matter of creating an instance of something that implements the following interface: .. code-block:: python :linenos: class IAuthenticationPolicy(object): """ An object representing a Pyramid authentication policy. """ def authenticated_userid(self, request): """ Return the authenticated userid or ``None`` if no authenticated userid can be found. This method of the policy should ensure that a record exists in whatever persistent store is used related to the user (the user should not have been deleted); if a record associated with the current id does not exist in a persistent store, it should return ``None``.""" def unauthenticated_userid(self, request): """ Return the *unauthenticated* userid. This method performs the same duty as ``authenticated_userid`` but is permitted to return the userid based only on data present in the request; it needn't (and shouldn't) check any persistent store to ensure that the user record related to the request userid exists.""" def effective_principals(self, request): """ Return a sequence representing the effective principals including the userid and any groups belonged to by the current user, including 'system' groups such as ``pyramid.security.Everyone`` and ``pyramid.security.Authenticated``. """ def remember(self, request, principal, **kw): """ Return a set of headers suitable for 'remembering' the principal named ``principal`` when set in a response. An individual authentication policy and its consumers can decide on the composition and meaning of **kw. """ def forget(self, request): """ Return a set of headers suitable for 'forgetting' the current user on subsequent requests. """ After you do so, you can pass an instance of such a class into the :class:`~pyramid.config.Configurator.set_authentication_policy` method configuration time to use it. .. index:: single: authorization policy (creating) .. _creating_an_authorization_policy: Creating Your Own Authorization Policy -------------------------------------- An authorization policy is a policy that allows or denies access after a user has been authenticated. Most :app:`Pyramid` applications will use the default :class:`pyramid.authorization.ACLAuthorizationPolicy`. However, in some cases, it's useful to be able to use a different authorization policy than the default :class:`~pyramid.authorization.ACLAuthorizationPolicy`. For example, it might be desirable to construct an alternate authorization policy which allows the application to use an authorization mechanism that does not involve :term:`ACL` objects. :app:`Pyramid` ships with only a single default authorization policy, so you'll need to create your own if you'd like to use a different one. Creating and using your own authorization policy is a matter of creating an instance of an object that implements the following interface: .. code-block:: python :linenos: class IAuthorizationPolicy(object): """ An object representing a Pyramid authorization policy. """ def permits(self, context, principals, permission): """ Return ``True`` if any of the ``principals`` is allowed the ``permission`` in the current ``context``, else return ``False`` """ def principals_allowed_by_permission(self, context, permission): """ Return a set of principal identifiers allowed by the ``permission`` in ``context``. This behavior is optional; if you choose to not implement it you should define this method as something which raises a ``NotImplementedError``. This method will only be called when the ``pyramid.security.principals_allowed_by_permission`` API is used.""" After you do so, you can pass an instance of such a class into the :class:`~pyramid.config.Configurator.set_authorization_policy` method at configuration time to use it.