.. -*- coding: utf-8 -*-

The security model

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The main principles are:

* users and groups of users

* a user belongs to at least one group of user

* permissions (read, update, create, delete)

* permissions are assigned to groups (and not to users)

For *CubicWeb* in particular:

* we associate rights at the enttities/relations schema level

* for each entity, we distinguish four kind of permissions: read,

  add, update and delete

* for each relation, we distinguish three king of permissions: read,

  add and delete (we can not modify a relation)

* the basic groups are: Administrators, Users and Guests

* by default, users belongs to the group Users

* there is a virtual group called `Owners users` to which we

  can associate only deletion and update permissions

* we can not add users to the `Owners users` group, they are

  implicetely added to it according to the context of the objects

  they own

* the permissions of this group are only be checked on update/deletion

  actions if all the other groups the user belongs does not provide

  those permissions

Permissions definition

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Setting permissions is done with the attribute `permissions` of entities and

relation types. It defines a dictionary where the keys are the access types

(action), and the values are the authorized groups or expressions.

For an entity type, the possible actions are `read`, `add`, `update` and

`delete`.

For a relation type, the possible actions are `read`, `add`, and `delete`.

For each access type, a tuple indicates the name of the authorized groups and/or

one or multiple RQL expressions to satisfy to grant access. The access is

provided once the user is in the listed groups or one of the RQL condition is

satisfied.

The standard groups are :

* `guests`

* `users`

* `managers`

* `owners` : virtual group corresponding to the entity's owner.

  This can only be used for the actions `update` and `delete` of an entity

  type.

of the cube (``migration/precreate.py``).

Use of RQL expression for writing rights

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(`add`, `delete` and `update`) on relation and entity types.

RQL expression for entity type permission :

* you have to use the class `ERQLExpression`

* the used expression corresponds to the WHERE statement of an RQL query

* in this expression, the variables X and U are pre-defined references

  respectively on the current entity (on which the action is verified) and

  on the user who send the request

  object is a any variable, meaning that the user needs to have

  permission to execute the action <ACTION> on the entities related

for the following :

* in the expression, the variables S, O and U are pre-defined references

  to respectively the subject and the object of the current relation (on

  which the action is being verified) and the user who executed the query

  - the permissions `add` and `delete` are equivalent. Only `add`/`read`

    are actually taken in consideration.

In addition to that the entity type `EPermission` from the standard library

this entity type is as follow : ::

	"""entity type that may be used to construct some advanced security configuration

	"""

Example of configuration ::

    ...

    class Version(EntityType):

	"""a version is defining the content of a particular project's release"""

	permissions = {'read':   ('managers', 'users', 'guests',),

		       'update': ('managers', 'logilab', 'owners',),

		       'delete': ('managers', ),

		       'add':    ('managers', 'logilab',

				  ERQLExpression('X version_of PROJ, U in_group G,'

						 'PROJ require_permission P, P name "add_version",'

						 'P require_group G'),)}

    ...

    class version_of(RelationType):

	"""link a version to its project. A version is necessarily linked to one and only one project.

	"""

	permissions = {'read':   ('managers', 'users', 'guests',),

		       'delete': ('managers', ),

		       'add':    ('managers', 'logilab',

				  RRQLExpression('O require_permission P, P name "add_version",'

						 'U in_group G, P require_group G'),)

		       }

	inlined = True

"add_version" can be associated to a project and provides rights to create

new versions on this project to specific groups. It is important to notice that :

* in such case, we have to protect both the entity type "Version" and the relation

  associating a version to a project ("version_of")

  a unification with the groups and/or the states if necessary in the expression

  ("U in_group G, P require_group G" in the above example)

Use of RQL expression for reading rights

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The principles are the same but with the following restrictions :

* we can not use `RRQLExpression` on relation types for reading

* special relations "has_<ACTION>_permission" can not be used

Note on the use of RQL expression for `add` permission

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Potentially, the use of an RQL expression to add an entity or a relation

can cause problems for the user interface, because if the expression uses

permissions before we actually add the entity (please note that this is

not a problem for the RQL server at all, because the permissions checks are

To compensate this problem, it is usually necessary, for such case,

to use an action that reflects the schema permissions but which enables

to check properly the permissions so that it would show up if necessary.