.. _TutosPhotoWebSiteSecurity:
Security, testing and migration
-------------------------------
This part will cover various topics:
* configuring security
* migrating existing instance
* writing some unit tests
Here is the ``read`` security model I want:
* folders, files, images and comments should have one of the following visibility:
- ``public``, everyone can see it
- ``authenticated``, only authenticated users can see it
- ``restricted``, only a subset of authenticated users can see it
* managers (e.g. me) can see everything
* only authenticated users can see people
* everyone can see classifier entities, such as tag and zone
Also, unless explicitly specified, the visibility of an image should be the same as
its parent folder, as well as visibility of a comment should be the same as the
commented entity. If there is no parent entity, the default visibility is
``authenticated``.
Regarding write security, that's much easier:
* anonymous can't write anything
* authenticated users can only add comment
* managers will add the remaining stuff
Now, let's implement that!
Proper security in CubicWeb is done at the schema level, so you don't have to
bother with it in views: users will only see what they can see automatically.
.. _adv_tuto_security:
Step 1: configuring security into the schema
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In schema, you can grant access according to groups, or to some RQL expressions:
users get access if the expression returns some results. To implement the read
security defined earlier, groups are not enough, we'll need some RQL expression. Here
is the idea:
* add a `visibility` attribute on Folder, File and Comment, which may be one of
the value explained above
* add a `may_be_read_by` relation from Folder, File and Comment to users,
which will define who can see the entity
* security propagation will be done in hook.
So the first thing to do is to modify my cube's schema.py to define those
relations:
.. sourcecode:: python
from yams.constraints import StaticVocabularyConstraint
class visibility(RelationDefinition):
subject = ('Folder', 'File', 'Comment')
object = 'String'
constraints = [StaticVocabularyConstraint(('public', 'authenticated',
'restricted', 'parent'))]
default = 'parent'
cardinality = '11' # required
class may_be_read_by(RelationDefinition):
__permissions__ = {
'read': ('managers', 'users'),
'add': ('managers',),
'delete': ('managers',),
}
subject = ('Folder', 'File', 'Comment',)
object = 'CWUser'
We can note the following points:
* we've added a new `visibility` attribute to folder, file, image and comment
using a `RelationDefinition`
* `cardinality = '11'` means this attribute is required. This is usually hidden
under the `required` argument given to the `String` constructor, but we can
rely on this here (same thing for StaticVocabularyConstraint, which is usually
hidden by the `vocabulary` argument)
* the `parent` possible value will be used for visibility propagation
* think to secure the `may_be_read_by` permissions, else any user can add/delete it
by default, which somewhat breaks our security model...
Now, we should be able to define security rules in the schema, based on these new
attribute and relation. Here is the code to add to *schema.py*:
.. sourcecode:: python
from cubicweb.schema import ERQLExpression
VISIBILITY_PERMISSIONS = {
'read': ('managers',
ERQLExpression('X visibility "public"'),
ERQLExpression('X may_be_read_by U')),
'add': ('managers',),
'update': ('managers', 'owners',),
'delete': ('managers', 'owners'),
}
AUTH_ONLY_PERMISSIONS = {
'read': ('managers', 'users'),
'add': ('managers',),
'update': ('managers', 'owners',),
'delete': ('managers', 'owners'),
}
CLASSIFIERS_PERMISSIONS = {
'read': ('managers', 'users', 'guests'),
'add': ('managers',),
'update': ('managers', 'owners',),
'delete': ('managers', 'owners'),
}
from cubes.folder.schema import Folder
from cubes.file.schema import File
from cubes.comment.schema import Comment
from cubes.person.schema import Person
from cubes.zone.schema import Zone
from cubes.tag.schema import Tag
Folder.__permissions__ = VISIBILITY_PERMISSIONS
File.__permissions__ = VISIBILITY_PERMISSIONS
Comment.__permissions__ = VISIBILITY_PERMISSIONS.copy()
Comment.__permissions__['add'] = ('managers', 'users',)
Person.__permissions__ = AUTH_ONLY_PERMISSIONS
Zone.__permissions__ = CLASSIFIERS_PERMISSIONS
Tag.__permissions__ = CLASSIFIERS_PERMISSIONS
What's important in there:
* `VISIBILITY_PERMISSIONS` provides read access to managers group, if
`visibility` attribute's value is 'public', or if user (designed by the 'U'
variable in the expression) is linked to the entity (the 'X' variable) through
the `may_be_read_by` permission
* we modify permissions of the entity types we use by importing them and
modifying their `__permissions__` attribute
* notice the `.copy()`: we only want to modify 'add' permission for `Comment`,
not for all entity types using `VISIBILITY_PERMISSIONS`!
* the remaining part of the security model is done using regular groups:
- `users` is the group to which all authenticated users will belong
- `guests` is the group of anonymous users
.. _adv_tuto_security_propagation:
Step 2: security propagation in hooks
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
To fullfill the requirements, we have to implement::
Also, unless explicity specified, visibility of an image should be the same as
its parent folder, as well as visibility of a comment should be the same as the
commented entity.
This kind of `active` rule will be done using CubicWeb's hook
system. Hooks are triggered on database events such as addition of a new
entity or relation.
The tricky part of the requirement is in *unless explicitly specified*, notably
because when the entity is added, we don't know yet its 'parent'
entity (e.g. Folder of an File, File commented by a Comment). To handle such things,
CubicWeb provides `Operation`, which allow to schedule things to do at commit time.
In our case we will:
* on entity creation, schedule an operation that will set default visibility
* when a "parent" relation is added, propagate parent's visibility unless the
child already has a visibility set
Here is the code in cube's *hooks.py*:
.. sourcecode:: python
from cubicweb.predicates import is_instance
from cubicweb.server import hook
class SetVisibilityOp(hook.DataOperationMixIn, hook.Operation):
def precommit_event(self):
for eid in self.get_data():
entity = self.session.entity_from_eid(eid)
if entity.visibility == 'parent':
entity.cw_set(visibility=u'authenticated')
class SetVisibilityHook(hook.Hook):
__regid__ = 'sytweb.setvisibility'
__select__ = hook.Hook.__select__ & is_instance('Folder', 'File', 'Comment')
events = ('after_add_entity',)
def __call__(self):
SetVisibilityOp.get_instance(self._cw).add_data(self.entity.eid)
class SetParentVisibilityHook(hook.Hook):
__regid__ = 'sytweb.setparentvisibility'
__select__ = hook.Hook.__select__ & hook.match_rtype('filed_under', 'comments')
events = ('after_add_relation',)
def __call__(self):
parent = self._cw.entity_from_eid(self.eidto)
child = self._cw.entity_from_eid(self.eidfrom)
if child.visibility == 'parent':
child.cw_set(visibility=parent.visibility)
Notice:
* hooks are application objects, hence have selectors that should match entity or
relation types to which the hook applies. To match a relation type, we use the
hook specific `match_rtype` selector.
* usage of `DataOperationMixIn`: instead of adding an operation for each added entity,
DataOperationMixIn allows to create a single one and to store entity's eids to be
processed in the transaction data. This is a good pratice to avoid heavy
operations manipulation cost when creating a lot of entities in the same
transaction.
* the `precommit_event` method of the operation will be called at transaction's
commit time.
* in a hook, `self._cw` is the repository session, not a web request as usually
in views
* according to hook's event, you have access to different attributes on the hook
instance. Here:
- `self.entity` is the newly added entity on 'after_add_entity' events
- `self.eidfrom` / `self.eidto` are the eid of the subject / object entity on
'after_add_relation' events (you may also get the relation type using
`self.rtype`)
The `parent` visibility value is used to tell "propagate using parent security"
because we want that attribute to be required, so we can't use None value else
we'll get an error before we get any chance to propagate...
Now, we also want to propagate the `may_be_read_by` relation. Fortunately,
CubicWeb provides some base hook classes for such things, so we only have to add
the following code to *hooks.py*:
.. sourcecode:: python
# relations where the "parent" entity is the subject
S_RELS = set()
# relations where the "parent" entity is the object
O_RELS = set(('filed_under', 'comments',))
class AddEntitySecurityPropagationHook(hook.PropagateRelationHook):
"""propagate permissions when new entity are added"""
__regid__ = 'sytweb.addentity_security_propagation'
__select__ = (hook.PropagateRelationHook.__select__
& hook.match_rtype_sets(S_RELS, O_RELS))
main_rtype = 'may_be_read_by'
subject_relations = S_RELS
object_relations = O_RELS
class AddPermissionSecurityPropagationHook(hook.PropagateRelationAddHook):
"""propagate permissions when new entity are added"""
__regid__ = 'sytweb.addperm_security_propagation'
__select__ = (hook.PropagateRelationAddHook.__select__
& hook.match_rtype('may_be_read_by',))
subject_relations = S_RELS
object_relations = O_RELS
class DelPermissionSecurityPropagationHook(hook.PropagateRelationDelHook):
__regid__ = 'sytweb.delperm_security_propagation'
__select__ = (hook.PropagateRelationDelHook.__select__
& hook.match_rtype('may_be_read_by',))
subject_relations = S_RELS
object_relations = O_RELS
* the `AddEntitySecurityPropagationHook` will propagate the relation
when `filed_under` or `comments` relations are added
- the `S_RELS` and `O_RELS` set as well as the `match_rtype_sets` selector are
used here so that if my cube is used by another one, it'll be able to
configure security propagation by simply adding relation to one of the two
sets.
* the two others will propagate permissions changes on parent entities to
children entities
.. _adv_tuto_tesing_security:
Step 3: testing our security
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Security is tricky. Writing some tests for it is a very good idea. You should
even write them first, as Test Driven Development recommends!
Here is a small test case that will check the basis of our security
model, in *test/unittest_sytweb.py*:
.. sourcecode:: python
from cubicweb.devtools.testlib import CubicWebTC
from cubicweb import Binary
class SecurityTC(CubicWebTC):
def test_visibility_propagation(self):
with self.admin_access.repo_cnx() as cnx:
# create a user for later security checks
toto = self.create_user(cnx, 'toto')
cnx.commit()
# init some data using the default manager connection
folder = cnx.create_entity('Folder',
name=u'restricted',
visibility=u'restricted')
photo1 = cnx.create_entity('File',
data_name=u'photo1.jpg',
data=Binary('xxx'),
filed_under=folder)
cnx.commit()
# visibility propagation
self.assertEquals(photo1.visibility, 'restricted')
# unless explicitly specified
photo2 = cnx.create_entity('File',
data_name=u'photo2.jpg',
data=Binary('xxx'),
visibility=u'public',
filed_under=folder)
cnx.commit()
self.assertEquals(photo2.visibility, 'public')
with self.new_access('toto').repo_cnx() as cnx:
# test security
self.assertEqual(1, len(cnx.execute('File X'))) # only the public one
self.assertEqual(0, len(cnx.execute('Folder X'))) # restricted...
with self.admin_access.repo_cnx() as cnx:
# may_be_read_by propagation
folder = cnx.entity_from_eid(folder.eid)
folder.cw_set(may_be_read_by=toto)
cnx.commit()
with self.new_access('toto').repo_cnx() as cnx:
photo1 = cnx.entity_from_eid(photo1.eid)
self.failUnless(photo1.may_be_read_by)
# test security with permissions
self.assertEquals(2, len(cnx.execute('File X'))) # now toto has access to photo2
self.assertEquals(1, len(cnx.execute('Folder X'))) # and to restricted folder
if __name__ == '__main__':
from logilab.common.testlib import unittest_main
unittest_main()
It's not complete, but shows most things you'll want to do in tests: adding some
content, creating users and connecting as them in the test, etc...
To run it type:
.. sourcecode:: bash
$ pytest unittest_sytweb.py
======================== unittest_sytweb.py ========================
-> creating tables [....................]
-> inserting default user and default groups.
-> storing the schema in the database [....................]
-> database for instance data initialized.
.
----------------------------------------------------------------------
Ran 1 test in 22.547s
OK
The first execution is taking time, since it creates a sqlite database for the
test instance. The second one will be much quicker:
.. sourcecode:: bash
$ pytest unittest_sytweb.py
======================== unittest_sytweb.py ========================
.
----------------------------------------------------------------------
Ran 1 test in 2.662s
OK
If you do some changes in your schema, you'll have to force regeneration of that
database. You do that by removing the tmpdb files before running the test: ::
$ rm data/database/tmpdb*
.. Note::
pytest is a very convenient utility used to control test execution. It is available from the `logilab-common`_ package.
.. _`logilab-common`: http://www.logilab.org/project/logilab-common
.. _adv_tuto_migration_script:
Step 4: writing the migration script and migrating the instance
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Prior to those changes, I created an instance, fed it with some data, so I
don't want to create a new one, but to migrate the existing one. Let's see how to
do that.
Migration commands should be put in the cube's *migration* directory, in a
file named file:`<X.Y.Z>_Any.py` ('Any' being there mostly for historical reasons).
Here I'll create a *migration/0.2.0_Any.py* file containing the following
instructions:
.. sourcecode:: python
add_relation_type('may_be_read_by')
add_relation_type('visibility')
sync_schema_props_perms()
Then I update the version number in the cube's *__pkginfo__.py* to 0.2.0. And
that's it! Those instructions will:
* update the instance's schema by adding our two new relations and update the
underlying database tables accordingly (the first two instructions)
* update schema's permissions definition (the last instruction)
To migrate my instance I simply type::
cubicweb-ctl upgrade sytweb_instance
You'll then be asked some questions to do the migration step by step. You should say
YES when it asks if a backup of your database should be done, so you can get back
to initial state if anything goes wrong...