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django-rbac

Introduction

First of all, I would like to show some drawbacks of Django's current permission system:

  • Permissions are tied directly to the User model from django.contrib.auth, so you cannot use any other existing model in your application.
  • The task of mantaining this list of permissions in the current Django system is responsibility of a superuser or some other kind of centralized entity.
  • You can certainly assign permissions to Group model instances, but all users in this group will share the same permissions.
  • Last, but not least, until Django v1.2 will come and ticket #11010_ implemented, the permission system is model-level -- it doesn't allow granular permissions (row-level), which means you can give a user authorization to do something based on all instances of a model class, but not to a single model instance (an object).

Many applications, and specially today's web applications -- which involve concepts as collaboration or content driven by the users -- need the flexibility to support delegation of permission granting to objects by other trusted agents. A clear example is a social networking site, where the users want to allow or deny access to their profiles or pictures, open or close their different communication channels like receiving friendship requests or private messages. django-rbac tries to champion this by introducing some key features from the Role-Based Access Control (RBAC) proposal. In this implementation users (subjects) are assigned different roles that, in turn, have (or not) privileges over objects. With this permission system, the owner of an object can give privileges to certain roles. For example, a user can grant access to other users trying to read some personal info only if they belong to, at least, one of the roles specified in the permission rule.

I initially developed the first version of this app for a social network, to give its users the ability to control who has privileges upon their profiles, photo albums, personal information, and such. If you are in a similar situation, you'll find that django-rbac suits perfect for your purposes. But, as long as a general-purpose access control is being implemented, even if you are building any other kind of application which needs this level of permission control, django-rbac will help you out. I think I have made it enough generic to match a wide range of use cases.

I you are interested, you can read the introduced formal model by F. Ferraiolo and D. R. Kuhn.

Dependencies

Be sure you have django.contrib.contenttypes installed in you project.

Installation

Mercurial checkout

Install Mercurial if you don't have it yet, and clone the repository:

hg clone http://bitbucket.org/nabucosound/django-nomadblog/

Symlink to the folder called rbac inside django-rbac from somewhere in your PYTHONPATH -- could be the system-wide site-packages python folder, or the path your virtualenv project is using, if you are using Virtualenv (which I strongly encourage). And if you do and are also using Virtualenvwrapper then you can easily add2virtualenv.

Overview

Permissions are constructed by the following elements:

1. The owner: The owner of either the object being accessed or the permission rule itself -- a site user, a community administrator... 3. The object: The element being accessed on which the permission is being checked upon -- a profile, photo album... 3. The operation: The action requested -- display, create, delete, show birth date, send message, request friendship... 4. The roles: Define who is the requesting user in relation to the owner or the object -- anonymous, friend, family, coworker, roommate...

This is best explained with a simple example:

  • User Fritz wants to see Mr. Natural's profile. Thus, Fritz requests permission to access (view) the profile for Mr. Natural (the object).

  • Fritz is initially an 'anonymous' user, a role that everybody holds in the system. As Fritz and Mr. Natural are friends, the role 'friend' is appended to the role set where 'anonymous' was also included.

  • The privacy framework performs its magic to pull an answer: has Fritz permission to access this profile?
    • For the 'anonymous' role, the system denies the access.
    • For the 'friend' role the access is granted, as Mr. Natural had set access only to friends to his profile.
  • Access is granted, so Fritz can go ahead and view all the stuff.

A permission can be assigned to a either a single object ("per-object permission" category, also known as "granular permissions" or "row level permissions") or to all objects of the same model class. For this reason, django-rbac implements two classes respectively: RBACPermission and RBACGenericPermission. The example above falls into the first "per-object permission" category.

How it works

First it is essential for you to know that in django-rbac, asking for permission is a 2-step process:

  1. Get the roles: The user that tries to perform the operation over an object or model does so within a context given between him and the owner or the object/model itself. You have to provide a python list of RBACRole objects to the function that will check authorization (point 2 in this list!)
  2. Call rbac_permission function: It will perform the checking to answer if the operation is authorized or not.

You are totally responsible of executing step 1. The ways that roles can be assigned to users and endless, particular to each application or project, so django-rbac cannot plan in advance any way of doing it generic. The resulting role list is then passed to the rbac_permission along with the object or model owner, the object or model itself, and the operation. More on this in the following sections.

Operations

The RBACOperation model define functions that can be done in the system, e.g. 'display_profile', 'send_message', 'request_friendship', or 'show_email'. You can define what you want, just try to stick to a common syntax convention and short names for your own sake, because these strings will be used later on to request authorizations over permissions in your code.

Roles

Originally a role is a job function within the context of an organization, but it can also be seen like a relationship between the requesting user (subject) and the owner. Users trying to perform operations over bjects can do so in multiple fashions. For example, someone asks for permission to see, let's say, a photo album from another user. Such requesting user can be friend or family of the album owner, a member of a photography community, or maybe an anonymous folk with a deep interest in other's pics. Thus, 'anonymous', 'friend', 'community_member' or 'family' would be roles that users can belong to.

Writing functions to get roles

Sometimes you need to provide your app some programming logic to know which roles is the requesting user going to play. A common case is the request.user in a Django view. See this example extracted from the project that comes with the django-rbac package in the example folder:

from rbac.models import RBACRole

def get_user_roles(user, target_user):
    roles = []
    # These two functions below would validate the relationship between the two users.
    # If any exist, append the corresponding role to the roles list to be returned.
    if users_are_friends(user, target_user):
        roles.append(RBACRole.objects.get(name='friend')) #Assuming 'friend' role object exists
    if users_are_coworkers(user, target_user):
        roles.append(RBACRole.objects.get(name='coworker')) #Assuming 'coworker' role object exists
    return roles

Permissions

Once you have your operations and roles ready, you can start creating permissions. RBAC enables the conditions for the implementaiton of what is called the Separation of Duties (SoD), so tipically applications or projects using django-rbac will set mechanisms to delegate creating new permissions to owners. That is, the owner of an object will be who is setting the permission level to all the operations that can be done with the object. You are again responsible of providing the user an interface to accomplish this task. Classical social networks, for example, give their users a 'privacy' page with forms to change different permission settings.

As mentioned in the Overview section, the scope of a permission can be row level (RBACPermission) or model class level (RBACGenericPermission). Both models receive:

  • The model instance of the permission owner, i.e. a User object.
  • An operation string from a known RBACOperation, i.e. 'display_profile'
  • A list of RBACRole objects
  • The object: RBACPermission receives a model instance (for example, a Group object), while RBACGenericPermission receives a class model (for example, a Group model).

Two things to keep in mind when planning your permissions:

  • django-rbac follows this golden rule: if a permission doesn't exist, the operation is denied. This is for convenience, because fewer permission objects need to be created.
  • Try to avoid defining permissions that contain mutually exclusive roles. For example, a permission could have 'friend' and 'anonymous user' into his list of roles. Obviously, the first allows the permission operation to everybody, while the second restricts an access only to friends.

Usage in views

The example folder is a Django project with a myapp app that contains a views.py. Inspect the code to see how you can integrate django-rbac in your views.

Usage in shell

# This use case is about defining a role-based access control system for users # who want to restrict group memberships and profile info access. >>> from rbac.models import RBACPermission, RBACRole # Create an operation to define who sees/displays what: >>> operation = RBACOperation.objects.create(name='display') # Create some roles: >>> RBACRole.objects.create(name='friend') <RBACRole: friend> >>> RBACRole.objects.create(name='coworker') <RBACRole: coworker> >>> RBACRole.objects.create(name='family') <RBACRole: family> # As an example of a generic permission (per-model permissions), # we will restrict access to all user groups only to certain roles >>> from django.contrib.auth.models import User, Group # Create a user that will act as the owner: >>> owner = User.objects.create(username='hector') # Add some groups to the owner: >>> group1 = Group.objects.create(name='punks') >>> group2 = Group.objects.create(name='rockers') >>> owner.groups.add(group1) >>> owner.groups.add(group2) # Create generic permission: hector (owner) allows his friends, coworkers # and family (roles) to display (operation) his groups (django Group model) >>> from rbac.models import RBACGenericPermission >>> roles = RBACRole.objects.all() >>> RBACGenericPermission.objects.create_permission(owner, Group, operation, roles) <RBACGenericPermission: hector | group | display> # To check if a user in a given role context is authorized to perform the operation # 'display', we use the rbac_permission function from utils: >>> from rbac.utils import rbac_permission >>> rbac_permission(owner, Group, 'display', roles) True # Create a new role and verivy that we are not allowed if trying to access # with only this role in the role list: >>> RBACRole.objects.create(name='classmate') <RBACRole: classmate> # Note below that, although we get only one role object, still we need to pass # it inside a queryset list >>> roles = RBACRole.objects.filter(name='classmate') >>> rbac_permission(owner, Group, 'display', roles) False # As an example of a per-object permission, we will restrict which roles # are allowed to display the owner's user details. >>> from rbac.models import RBACPermission # If no permission exists for a given scenario, rbac_permission returns False, # following the django-rbac golden rule: if a permission doesn't exist, the operation is denied. # Also note that we are passing a model instance >>> rbac_permission(owner, owner, 'display', roles) False # Create permission: hector (owner) allows only his friends (roles) to display (operation) # his user info (again, owner -- a django User model instance) >>> roles = RBACRole.objects.filter(name='friend') >>> RBACPermission.objects.create_permission(owner, owner, operation, roles) <RBACPermission: hector | hector | display> >>> rbac_permission(owner, owner, 'display', roles) True