Permissions

Kinto-Core provides a mechanism to handle authorization on the stored objects.

This section gives details about the behaviour of resources in regards to permissions.

Resource

from kinto.core import resource

@resource.register()
class Toadstool(resource.Resource):
    schema = MushroomSchema

With this resource class, Kinto-Core will register the endpoints with a specific route factory, that will take care of checking the appropriate permission for each action.

Method	URL	permission	Comments
GET / HEAD	/{resource}	read	If not allowed by setting kinto.{resource}_read_principals, will return list of records where user has read permission.
POST	/{resource}	create	Allowed by setting kinto.{resource}_create_principals
DELETE	/{resource}	write	If not allowed by setting kinto.{resource}_write_principals, will delete the list of records where user has write permission.
GET / HEAD	/{resource}/{id}	read	If not allowed by setting kinto.{resource}_read_principals, will check record permissions
PUT	/{resource}/{id}	create if record doesn’t exist, write otherwise	Allowed by setting kinto.{resource}_create_principals, or kinto.{resource}_create_principals or existing record permissions
PATCH	/{resource}/{id}	write	If not allowed by setting kinto.{resource}_write_principals, will check record permissions
DELETE	/{resource}/{id}	write	If not allowed by setting kinto.{resource}_write_principals, will check record permissions

The objects permissions can be manipulated via the permissions attribute in the JSON payload, aside the data attribute. It allows to specify the list of principals allowed for each permission, as detailed in the API section.

Important

When defining permissions, there are two specific principals:

• system.Authenticated: any authenticated user

• system.Everyone: any user

The write permission is required to be able to modify the permissions of an existing object.

When an object is created or modified, the current user is added to list of principals for the write permission on this object. That means that a user is always able to replace or delete the records she created.

Related/Inherited permissions

In the above section, the list of allowed principals for actions on the resource (especially create) is specified via settings.

It is possible to extend the previously described behavior with related permissions.

For example, having permission to create blog articles also means permission to write categories.

To do so, specify the get_bound_permissions of the Kinto-Core authorization policy.

def get_bound_permissions(self, permission_object_id, permission):
    related = [(permission_object_id, permission)]
    # Grant `read` if user can `write`
    if permission == 'write':
        related.append((permission_object_id, 'read'))
    return related

from pyramid.interfaces import IAuthorizationPolicy

def main(global_settings, **settings):
    ...
    kinto.core.initialize(config, __version__)
    ...
    authz = config.registry.queryUtility(IAuthorizationPolicy)
    authz.get_bound_permissions = get_bound_permissions

In Kinto, this is leveraged to implement an inheritance tree of permissions between nested objects. The root objects permissions still have to be specified via settings though.

It is also possible to subclass the default kinto.core.authorization.AuthorizationPolicy.

from kinto.core import authorization
from pyramid.interfaces import IAuthorizationPolicy
from zope.interface import implementer

@implementer(IAuthorizationPolicy)
class MyAuthz(authorization.AuthorizationPolicy):
    def get_bound_permissions(self, permission_object_id, permission):
        related = [(permission_object_id, permission)]
        # Grant permission on `categories` if permission on `articles`
        if permission_object_id.startswith('/articles'):
            related.append((permission_object_id + '/categories', permission))
        return related

This would require forcing the setting multiauth.authorization_policy = myapp.authz.MyAuthz.

Manipulate permissions

One way of achieving dynamic permissions is to manipulate the permission backend manually.

For example, in some imaginary admin view:

def admin_view(request):
    # Custom Pyramid view.
    permission = request.registry.permission

    # Give `create` permission to `user_id` in POST
    some_user_id = request.POST['user_id']
    permission_object_id = '/articles'
    permission = 'create'
    permission.add_principal_to_ace(permission_object_id,
                                    permission,
                                    some_user_id)

Or during application init (or scripts):

def main(global_config, **settings):
    # ...
    kinto.core.initialize(config, __version__)
    # ...

    some_user_id = 'ldap:alice@corp.com'
    permission_object_id = '/articles'
    permission = 'create'
    config.registry.permission.add_principal_to_ace(permission_object_id,
                                                    permission,
                                                    some_user_id)

Since principals can be anything, it is also possible to use them to define groups:

def add_to_admins(request):
    # Custom Pyramid view.
    permission = request.registry.permission

    some_user_id = request.POST['user_id']
    group_name = 'group:admins'
    permission.add_user_principal(some_user_id, group_name)

And then refer as group:admins in the list of allowed principals.

Custom permission checking

The permissions verification in Kinto-Core is done with usual Pyramid authorization abstractions. Most notably using an implementation of a RootFactory in conjonction with an Authorization policy.

In order to completely override (or mimic) the defaults, a custom RootFactory and a custom Authorization policy can be plugged on the resource during registration.

from kinto.core import resource

class MyViewSet(resource.ViewSet):

    def get_view_arguments(self, endpoint_type, resource_cls, method):
        args = super().get_view_arguments(endpoint_type,
                                          resource_cls,
                                          method)
        if method.lower() not in ('get', 'head'):
            args['permission'] = 'publish'
        return args

    def get_service_arguments(self):
        args = super().get_service_arguments()
        args['factory'] = myapp.MyRootFactory
        return args


@resource.register(viewset=MyViewSet())
class Resource(resource.Resource):
    schema = BookmarkSchema

See more details about available customization in the viewset section.

A custom RootFactory and AuthorizationPolicy should implement the permission checking using Pyramid mecanisms.

For example, a simplistic example with the previous resource viewset:

from pyramid.interfaces import IAuthorizationPolicy

class MyRootFactory:
    def __init__(self, request):
        self.current_resource = None
        service = request.current_service
        if service and hasattr(service, 'resource'):
            self.current_resource = service.resource


@implementer(IAuthorizationPolicy)
class AuthorizationPolicy:
    def permits(self, context, principals, permission):
        if context.current_resource == BlogArticle:
            if permission == 'publish':
                return 'group:publishers' in principals
        return False

class kinto.core.authorization.AuthorizationPolicy

Default authorization class, that leverages the permission backend for shareable resources.

get_bound_permissions = None

Callable that takes an object id and a permission and returns a list of tuples (<object id>, <permission>). Useful when objects permission depend on others.

Backends

The ACLs are stored in a permission backend. Like for Storage and Cache, it is pluggable from configuration.

PostgreSQL

class kinto.core.permission.postgresql.Permission(client, *args, **kwargs)

Permission backend using PostgreSQL.

Enable in configuration:

kinto.permission_backend = kinto.core.permission.postgresql

Database location URI can be customized:

kinto.permission_url = postgresql://user:pass@db.server.lan:5432/dbname

Alternatively, username and password could also rely on system user ident or even specified in ~/.pgpass (see PostgreSQL documentation).

Note

Some tables and indices are created when kinto migrate is run. This requires some privileges on the database, or some error will be raised.

Alternatively, the schema can be initialized outside the python application, using the SQL file located in kinto/core/permission/postgresql/schema.sql. This allows to distinguish schema manipulation privileges from schema usage.

A connection pool is enabled by default:

kinto.permission_pool_size = 10
kinto.permission_maxoverflow = 10
kinto.permission_max_backlog = -1
kinto.permission_pool_recycle = -1
kinto.permission_pool_timeout = 30
kinto.cache_poolclass =
    kinto.core.storage.postgresql.pool.QueuePoolWithMaxBacklog

The max_backlog limits the number of threads that can be in the queue waiting for a connection. Once this limit has been reached, any further attempts to acquire a connection will be rejected immediately, instead of locking up all threads by keeping them waiting in the queue.

See dedicated section in SQLAlchemy documentation for default values and behaviour.

Note

Using a dedicated connection pool is still recommended to allow load balancing, replication or limit the number of connections used in a multi-process deployment.

Noindex

Redis

See Kinto Redis driver plugin repository for more information.

Memory

class kinto.core.permission.memory.Permission(*args, **kwargs)

Permission backend implementation in local process memory.

Enable in configuration:

kinto.permission_backend = kinto.core.permission.memory

Noindex

API

Implementing a custom permission backend consists in implementating the following interface: