Drafted documentation for object-based permissions

docs/administration/permissions.md

@@ -0,0 +1,76 @@
+# Permissions
+
+NetBox v2.9 introduced a new object-based permissions framework, which replace's Django's built-in permission model. Object-based permissions allow for the assignment of permissions to an arbitrary subset of objects of a certain type, rather than only by type of object. For example, it is possible to grant a user permission to view only sites within a particular region, or to modify only VLANs with a numeric ID within a certain range.
+
+Assigning a permission in NetBox entails defining a relationship among several components:
+
+* Model(s) - One or more types of object in NetBox
+* User(s) - One or more users or groups of users
+* Actions - The actions that can be performed (view, add, change, and/or delete)
+* Attributes - An arbitrary filter used to limit the action to a specific subset of objects
+
+At a minimum, a permission assignment must specify one model, one user or group, and one action. The specification of constraining attributes is optional: A permission without any attributes specified will apply to all instances of the selected model(s).
+
+## Actions
+
+There are four core actions that can be permitted for each type of object within NetBox, roughly analogous to the CRUD convention (create, read, update, and delete):
+
+* View - Retrieve an object from the database
+* Add - Create a new object
+* Change - Modify an existing object
+* Delete - Delete an existing object
+
+Some models introduce additional permissions that can be granted to allow other actions. For example, the `napalm_read` permission on the device model allows a user to execute NAPALM queries on a device via NetBox's REST API. These can be specified when granting a permission in the "additional actions" field.
+
+## Attributes
+
+Constraining attributes are defined as a JSON object representing a [Django query filter](https://docs.djangoproject.com/en/stable/ref/models/querysets/#field-lookups). This is the same syntax that you would pass to the QuerySet `filter()` method when performing a query using the Django ORM. As with query filters, double underscores can be used to traverse related objects or invoke lookup expressions. Some example queries and their corresponding definitions are shown below.
+
+All attributes defined on a permission are applied with a logic AND. For example, suppose you assign a permission for the site model with the following attributes.
+
+```json
+{
+  "status": "active",
+  "region__name": "Americas"
+}
+```
+
+The permission will grant access only to sites which have a status of "active" **and** which are assigned to the "Americas" region. To achieve a logical OR with a different set of attributes, simply create another permission assignment for the same model and user/group. 
+
+### Example Attribute Definitions
+
+| Query Filter | Permission Attributes |
+| ------------ | --------------------- |
+| `filter(status='active')` | `{"status": "active"}` |
+| `filter(status='active', role='testing')` | `{"status": "active", "role": "testing"}` |
+| `filter(status__in=['planned', 'reserved'])` | `{"status__in": ["planned", "reserved"]}` |
+| `filter(name__startswith('Foo')` | `{"name__startswith": "Foo"}` |
+| `filter(vid__gte=100, vid__lt=200)` | `{"vid__gte": 100, "vid__lt": 200}` |
+
+## Permissions Enforcement
+
+### Viewing Objects
+
+Object-based permissions work by filtering the database query generated by a user's request to restrict the set of objects returned. When a request is received, NetBox first determines whether the user is authenticated and has been granted to perform the requested action. For example, if the requested URL is `/dcim/devices/`, NetBox will check for the `dcim.view_device` permission. If the user has not been assigned this permission (either directly or via a group assignment), NetBox will return a 403 (forbidden) HTTP response.
+
+If the permission has been granted, NetBox will compile any specified constraints for the model and action. For example, suppose two permissions have been assigned to the user granting view access to the device model, with the following constraints:
+
+```json
+[
+    {"site__name__in":  ["NYC1", "NYC2"]},
+    {"status":  "offline", "tenant__isnull":  true}
+]
+```
+
+This grants the user access to view any device that is in NYC1 or NYC2, **or** which has a status of "offline" and has no tenant assigned. These attributes will result in the following ORM query:
+
+```no-highlight
+Site.objects.filter(
+    Q(site__name__in=['NYC1', 'NYC2']),
+    Q(status='active', tenant__isnull=True)
+)
+```
+
+### Creating and Modifying Objects
+
+The same sort of logic is in play when a user attempts to create or modify an object in NetBox, with a twist. Once validation has completed, NetBox starts an atomic database transaction to facilitate the change, and the object is created or saved normally. Next, still within the transaction, NetBox issues a second query to retrieve the newly created/updated object, filtering the restricted queryset with the object's primary key. If this query fails to return the object, NetBox knows that the new revision does not match the attributes granted by the permission. The transaction is then aborted, and the database is left in its original state.

mkdocs.yml

@@ -58,6 +58,7 @@ nav:
         - Using Plugins: 'plugins/index.md'
         - Developing Plugins: 'plugins/development.md'
     - Administration:
+        - Permissions: 'administration/permissions.md'
         - Replicating NetBox: 'administration/replicating-netbox.md'
         - NetBox Shell: 'administration/netbox-shell.md'
     - API: