Classic Zope Security Policy
============================

This package implements a role-based security policy similar to the
policy found in Zope 2.  The security policy is responsible for
deciding whether an interaction has a permission on an object.  This
security policy does this using grant and denial information.  Managers
can grant or deny:

  - roles to principals,

  - permissions to principals, and

  - permissions to roles

Grants and denials are stored as annotations on objects.  To store
grants and denials, objects must be annotatable:

  >>> import zope.interface
  >>> from zope.app.annotation.interfaces import IAttributeAnnotatable
  >>> class Ob:
  ...     zope.interface.implements(IAttributeAnnotatable)

  >>> ob = Ob()

We use objects to represent principals.  These objects implement an
interface named `IPrincipal`, but the security policy only uses the `id`
and `groups` attributes:

  >>> class Principal:
  ...     def __init__(self, id):
  ...         self.id = id
  ...         self.groups = []

  >>> principal = Principal('bob')

Roles and permissions are also represented by objects, however, for
the purposes of the security policy, only string `ids` are used.

The security policy provides a factory for creating interactions:

  >>> import zope.app.securitypolicy.zopepolicy
  >>> interaction = zope.app.securitypolicy.zopepolicy.ZopeSecurityPolicy()

An interaction represents a specific interaction between some
principals (normally users) and the system.  Normally, we are only
concerned with the interaction of one principal with the system, although
we can have interactions of multiple principals.  Multiple-principal
interactions normally occur when untrusted users store code on a
system for later execution.  When untrusted code is executing, the
authors of the code participate in the interaction.  An
interaction has a permission on an object only if all of the
principals participating in the interaction have access to the object.

The `checkPermission` method on interactions is used to test whether
an interaction has a permission for an object.  An interaction without
participants always has every permission:

  >>> interaction.checkPermission('P1', ob)
  True

In this example, 'P1' is a permission id.

Normally, interactions have participants:

  >>> class Participation:
  ...     interaction = None
  >>> participation = Participation()
  >>> participation.principal = principal
  >>> interaction.add(participation)

If we have participants, then we don't have a permission unless there
are grants:

  >>> interaction.checkPermission('P1', ob)
  False

Note, however, that we always have the CheckerPublic permission:

  >>> from zope.security.checker import CheckerPublic
  >>> interaction.checkPermission(CheckerPublic, ob)
  True

We make grants and denials on objects by adapting them to various
granting interfaces.  The objects returned from the adaptation are 
object-specific manager objects:

  >>> from zope.app.securitypolicy import interfaces
  >>> roleper  = interfaces.IRolePermissionManager(ob)
  >>> prinrole = interfaces.IPrincipalRoleManager(ob)
  >>> prinper  = interfaces.IPrincipalPermissionManager(ob)

The computations involved in checking permissions can be
significant. To reduce the computational cost, caching is used
extensively. We could invalidate the cache as we make grants, but the
adapters for making grants will automatically invalidate the cache of
the current interaction.  They use the security-management apis to do
this. To take advantage of the cache invalidation, we'll need to let
the security-management system manage our interactions.  First, we'll
set our security policy as the default:

  >>> import zope.security.management
  >>> oldpolicy = zope.security.management.setSecurityPolicy(
  ...      zope.app.securitypolicy.zopepolicy.ZopeSecurityPolicy)

and then we'll create a new interaction:

  >>> participation = Participation()
  >>> participation.principal = principal
  >>> zope.security.management.newInteraction(participation)
  >>> interaction = zope.security.management.getInteraction()

We normally provide access by granting permissions to roles for an object:

  >>> roleper.grantPermissionToRole('P1', 'R1')

and then granting roles to principals for an object (local roles):

  >>> prinrole.assignRoleToPrincipal('R1', 'bob')

The combination of these grants, which we call a role-based grant,
provides the permission:

  >>> interaction.checkPermission('P1', ob)
  True

We can also provide a permission directly:

  >>> prinper.grantPermissionToPrincipal('P2', 'bob')
  >>> interaction.checkPermission('P2', ob)
  True

Permission grants or denials override role-based grant or denials.  So
if we deny P1:

  >>> prinper.denyPermissionToPrincipal('P1', 'bob')

we cause the interaction to lack the permission, despite the role
grants:

  >>> interaction.checkPermission('P1', ob)
  False

Similarly, even if we have a role-based denial of P2:

  >>> roleper.denyPermissionToRole('P2', 'R1')

we still have access, because of the permission-based grant:

  >>> interaction.checkPermission('P2', ob)
  True

A role-based denial doesn't actually deny a permission; rather it
prevents the granting of a permission. So, if we have both grants and
denials based on roles, we have access:

  >>> roleper.grantPermissionToRole('P3', 'R1')
  >>> roleper.grantPermissionToRole('P3', 'R2')
  >>> roleper.denyPermissionToRole('P3', 'R3')
  >>> prinrole.removeRoleFromPrincipal('R2', 'bob')
  >>> prinrole.assignRoleToPrincipal('R3', 'bob')

  >>> interaction.checkPermission('P3', ob)
  True

Global grants
-------------

Grants made to an object are said to be "local".  We can also make
global grants:

  >>> from zope.app.securitypolicy.rolepermission \
  ...     import rolePermissionManager as roleperG
  >>> from zope.app.securitypolicy.principalpermission \
  ...     import principalPermissionManager as prinperG
  >>> from zope.app.securitypolicy.principalrole \
  ...     import principalRoleManager as prinroleG

And the same rules apply to global grants and denials.

  >>> roleperG.grantPermissionToRole('P1G', 'R1G', False)

In these tests, we aren't bothering to define any roles, permissions,
or principals, so we pass an extra argument that tells the granting
routines not to check the validity of the values.

  >>> prinroleG.assignRoleToPrincipal('R1G', 'bob', False)
  >>> interaction.checkPermission('P1G', ob)
  True

  >>> prinperG.grantPermissionToPrincipal('P2G', 'bob', False)
  >>> interaction.checkPermission('P2G', ob)
  True

  >>> prinperG.denyPermissionToPrincipal('P1G', 'bob', False)
  >>> interaction.checkPermission('P1G', ob)
  False

  >>> roleperG.denyPermissionToRole('P2G', 'R1G', False)
  >>> interaction.checkPermission('P2G', ob)
  True

  >>> roleperG.grantPermissionToRole('P3G', 'R1G', False)
  >>> roleperG.grantPermissionToRole('P3G', 'R2G', False)
  >>> roleperG.denyPermissionToRole('P3G', 'R3G', False)
  >>> prinroleG.removeRoleFromPrincipal('R2G', 'bob', False)
  >>> prinroleG.assignRoleToPrincipal('R3G', 'bob', False)
  >>> interaction.checkPermission('P3G', ob)
  True

Local versus global grants
--------------------------

We, of course, acquire global grants by default:

  >>> interaction.checkPermission('P1G', ob)
  False
  >>> interaction.checkPermission('P2G', ob)
  True
  >>> interaction.checkPermission('P3G', ob)
  True

Local role-based grants do not override global principal-specific denials:

  >>> roleper.grantPermissionToRole('P1G', 'R1G')
  >>> prinrole.assignRoleToPrincipal('R1G', 'bob')
  >>> interaction.checkPermission('P1G', ob)
  False

And local role-based denials don't override global
principal-grants:

  >>> roleper.denyPermissionToRole('P2G', 'R1G')
  >>> interaction.checkPermission('P2G', ob)
  True

A local role-based deny can cancel a global role-based grant:

  >>> roleper.denyPermissionToRole('P3G', 'R1G')
  >>> interaction.checkPermission('P3G', ob)
  False

and a local role-based grant can override a global role-based denial:

  >>> roleperG.denyPermissionToRole('P4G', 'R1G', False)
  >>> prinroleG.assignRoleToPrincipal('R1G', "bob", False)
  >>> interaction.checkPermission('P4G', ob)
  False
  >>> roleper.grantPermissionToRole('P4G', 'R1G')
  >>> interaction.checkPermission('P4G', ob)
  True
  >>> prinroleG.removeRoleFromPrincipal('R1G', "bob", False)
  >>> interaction.checkPermission('P4G', ob)
  True

Of course, a local permission-based grant or denial overrides any
global setting and overrides local role-based grants or denials:

  >>> prinper.grantPermissionToPrincipal('P3G', 'bob')
  >>> interaction.checkPermission('P3G', ob)
  True

  >>> prinper.denyPermissionToPrincipal('P2G', 'bob')
  >>> interaction.checkPermission('P2G', ob)
  False

Sublocations
------------

We can have sub-locations. A sublocation of a location is an object
whose `__parent__` attribute is the location:

  >>> ob2 = Ob()
  >>> ob2.__parent__ = ob

By default, sublocations acquire grants from higher locations:

  >>> interaction.checkPermission('P1', ob2)
  False
  >>> interaction.checkPermission('P2', ob2)
  True
  >>> interaction.checkPermission('P3', ob2)
  True
  >>> interaction.checkPermission('P1G', ob2)
  False
  >>> interaction.checkPermission('P2G', ob2)
  False
  >>> interaction.checkPermission('P3G', ob2)
  True
  >>> interaction.checkPermission('P4G', ob2)
  True

Sublocation role-based grants do not override their parent
principal-specific denials:

  >>> roleper2  = interfaces.IRolePermissionManager(ob2)
  >>> prinrole2 = interfaces.IPrincipalRoleManager(ob2)
  >>> prinper2  = interfaces.IPrincipalPermissionManager(ob2)

  >>> roleper2.grantPermissionToRole('P1', 'R1')
  >>> prinrole2.assignRoleToPrincipal('R1', 'bob')
  >>> interaction.checkPermission('P1', ob2)
  False

And local role-based denials don't override their parents
principal-grant:

  >>> roleper2.denyPermissionToRole('P2', 'R1')
  >>> interaction.checkPermission('P2', ob2)
  True

A local role-based deny can cancel a parent role-based grant:

  >>> roleper2.denyPermissionToRole('P3', 'R1')
  >>> interaction.checkPermission('P3', ob2)
  False

and a local role-based grant can override a parent role-based denial:

  >>> roleper.denyPermissionToRole('P4', 'R1')
  >>> prinrole.assignRoleToPrincipal('R1', 'bob')
  >>> interaction.checkPermission('P4', ob2)
  False
  >>> roleper2.grantPermissionToRole('P4', 'R1')
  >>> interaction.checkPermission('P4', ob2)
  True
  >>> prinrole.removeRoleFromPrincipal('R1', 'bob')
  >>> interaction.checkPermission('P4', ob2)
  True


Of course, a local permission-based grant or denial overrides any
global setting and overrides local role-based grants or denials:

  >>> prinper.grantPermissionToPrincipal('P3', 'bob')
  >>> interaction.checkPermission('P3', ob2)
  True

  >>> prinper.denyPermissionToPrincipal('P2', 'bob')
  >>> interaction.checkPermission('P2', ob2)
  False

If an object is not annotatable, but does have a parent, it will get
its grants from its parent:

  >>> class C:
  ...     pass

  >>> ob3 = C()
  >>> ob3.__parent__ = ob

  >>> interaction.checkPermission('P1', ob3)
  False
  >>> interaction.checkPermission('P2', ob3)
  False
  >>> interaction.checkPermission('P3', ob3)
  True
  >>> interaction.checkPermission('P1G', ob3)
  False
  >>> interaction.checkPermission('P2G', ob3)
  False
  >>> interaction.checkPermission('P3G', ob3)
  True
  >>> interaction.checkPermission('P4G', ob3)
  True

The same results will be had if there are multiple non-annotatable
objects:

  >>> ob3.__parent__ = C()
  >>> ob3.__parent__.__parent__ = ob

  >>> interaction.checkPermission('P1', ob3)
  False
  >>> interaction.checkPermission('P2', ob3)
  False
  >>> interaction.checkPermission('P3', ob3)
  True
  >>> interaction.checkPermission('P1G', ob3)
  False
  >>> interaction.checkPermission('P2G', ob3)
  False
  >>> interaction.checkPermission('P3G', ob3)
  True
  >>> interaction.checkPermission('P4G', ob3)
  True

and if an object doesn't have a parent:

  >>> ob4 = C()

it will have whatever grants were made globally:

  >>> interaction.checkPermission('P1', ob4)
  False
  >>> interaction.checkPermission('P2', ob4)
  False
  >>> interaction.checkPermission('P3', ob4)
  False
  >>> interaction.checkPermission('P1G', ob4)
  False
  >>> interaction.checkPermission('P2G', ob4)
  True
  >>> interaction.checkPermission('P3G', ob4)
  False
  >>> interaction.checkPermission('P4G', ob4)
  False

  >>> prinroleG.assignRoleToPrincipal('R1G', "bob", False)
  >>> interaction.checkPermission('P3G', ob4)
  True

We'll get the same result if we have a non-annotatable parent without a
parent:

  >>> ob3.__parent__ = C()

  >>> interaction.checkPermission('P1', ob3)
  False
  >>> interaction.checkPermission('P2', ob3)
  False
  >>> interaction.checkPermission('P3', ob3)
  False
  >>> interaction.checkPermission('P1G', ob3)
  False
  >>> interaction.checkPermission('P2G', ob3)
  True
  >>> interaction.checkPermission('P3G', ob3)
  True
  >>> interaction.checkPermission('P4G', ob3)
  False

The Anonymous role
------------------

The security policy defines a special role named "zope.Anonymous".  All
principals have this role and the role cannot be taken away.

  >>> roleperG.grantPermissionToRole('P5', 'zope.Anonymous', False)
  >>> interaction.checkPermission('P5', ob2)
  True

Proxies
-------

Objects may be proxied:

  >>> from zope.security.checker import ProxyFactory
  >>> ob = ProxyFactory(ob)
  >>> interaction.checkPermission('P1', ob)
  False
  >>> interaction.checkPermission('P2', ob)
  False
  >>> interaction.checkPermission('P3', ob)
  True
  >>> interaction.checkPermission('P1G', ob)
  False
  >>> interaction.checkPermission('P2G', ob)
  False
  >>> interaction.checkPermission('P3G', ob)
  True
  >>> interaction.checkPermission('P4G', ob)
  True

as may their parents:

  >>> ob3 = C()
  >>> ob3.__parent__ = ob

  >>> interaction.checkPermission('P1', ob3)
  False
  >>> interaction.checkPermission('P2', ob3)
  False
  >>> interaction.checkPermission('P3', ob3)
  True
  >>> interaction.checkPermission('P1G', ob3)
  False
  >>> interaction.checkPermission('P2G', ob3)
  False
  >>> interaction.checkPermission('P3G', ob3)
  True
  >>> interaction.checkPermission('P4G', ob3)
  True

Groups
------

Principals may have groups.  Groups are also principals (and, thus,
may have groups).

If a principal has groups, the groups are available as group ids in
the principal's `groups` attribute.  The interaction has to convert
these group ids to group objects, so that it can tell whether the
groups have groups.  It does this by calling the `getPrincipal` method
on the principal authentication service, which is responsible for,
among other things, converting a principal id to a principal.
For our examples here, we'll create and register a stub principal
authentication service:

  >>> from zope.app.security.interfaces import IAuthentication
  >>> class FauxPrincipals(dict):
  ...     zope.interface.implements(IAuthentication)
  ...     def getPrincipal(self, id):
  ...         return self[id]

  >>> auth = FauxPrincipals()

  >>> from zope.app.testing import ztapi
  >>> ztapi.provideUtility(IAuthentication, auth)
  >>> from zope.app import zapi

Let's define a group:

  >>> auth['g1'] = Principal('g1')

Let's put the principal in our group.  We do that by adding the group id
to the new principals groups:

  >>> principal.groups.append('g1')

Of course, the principal doesn't have permissions not granted:

  >>> interaction.checkPermission('gP1', ob)
  False

Now, if we grant a permission to the group:

  >>> prinper.grantPermissionToPrincipal('gP1', 'g1')

We see that our principal has the permission:

  >>> interaction.checkPermission('gP1', ob)
  True

This works even if the group grant is global:

  >>> interaction.checkPermission('gP1G', ob)
  False

  >>> prinperG.grantPermissionToPrincipal('gP1G', 'g1', True)

  >>> interaction.checkPermission('gP1G', ob)
  True

Grants are, of course, acquired:

  >>> interaction.checkPermission('gP1', ob2)
  True

  >>> interaction.checkPermission('gP1G', ob2)
  True

Inner grants can override outer grants:

  >>> prinper2.denyPermissionToPrincipal('gP1', 'g1')
  >>> interaction.checkPermission('gP1', ob2)
  False

But principal grants always trump group grants:

  >>> prinper2.grantPermissionToPrincipal('gP1', 'bob')
  >>> interaction.checkPermission('gP1', ob2)
  True

Groups can have groups too:

  >>> auth['g2'] = Principal('g2')
  >>> auth['g1'].groups.append('g2')

If we grant to the new group:

  >>> prinper.grantPermissionToPrincipal('gP2', 'g2')

Then we, of course have that permission too:

  >>> interaction.checkPermission('gP2', ob2)
  True

Just as principal grants override group grants, group grants can
override other group grants:

  >>> prinper.denyPermissionToPrincipal('gP2', 'g1')
  >>> interaction.checkPermission('gP2', ob2)
  False

Principals can be in more than one group. Let's define a new group:

  >>> auth['g3'] = Principal('g3')
  >>> principal.groups.append('g3')
  >>> prinper.grantPermissionToPrincipal('gP2', 'g3')

Now, the principal has two groups. In one group, the permission 'gP2'
is denied, but in the other, it is allowed.  In a case like this, the
permission is allowed:

  >>> interaction.checkPermission('gP2', ob2)
  True

In a case where a principal has two or more groups, the group denies
prevent allows from their parents. They don't prevent the principal
from getting an allow from another principal.

Grants can be inherited from ancestor groups through multiple paths.
Let's grant a permission to g2 and deny it to g1:

  >>> prinper.grantPermissionToPrincipal('gP3', 'g2')
  >>> prinper.denyPermissionToPrincipal('gP3', 'g1')

Now, as before, the deny in g1 blocks the grant in g2:

  >>> interaction.checkPermission('gP3', ob2)
  False

Let's make g2 a group of g3:

  >>> auth['g3'].groups.append('g2')

Now, we get g2's grant through g3, and access is allowed:

  >>> interaction.invalidate_cache()
  >>> interaction.checkPermission('gP3', ob2)
  True

We can assign roles to groups:

  >>> prinrole.assignRoleToPrincipal('gR1', 'g2')

and get permissions through the roles:

  >>> roleper.grantPermissionToRole('gP4', 'gR1')
  >>> interaction.checkPermission('gP4', ob2)
  True

we can override role assignments to groups through subgroups:

  >>> prinrole.removeRoleFromPrincipal('gR1', 'g1')
  >>> prinrole.removeRoleFromPrincipal('gR1', 'g3')
  >>> interaction.checkPermission('gP4', ob2)
  False

and through principals:

  >>> prinrole.assignRoleToPrincipal('gR1', 'bob')
  >>> interaction.checkPermission('gP4', ob2)
  True

Cleanup
-------

We clean up the changes we made in these examples:

  >>> zope.security.management.endInteraction()
  >>> ignore = zope.security.management.setSecurityPolicy(oldpolicy)
