awx/docs/rbac.md

Role-Based Access Control (RBAC)

This document describes the RBAC implementation of the Ansible Tower Software. The intended audience of this document is the Ansible Tower developer.

Overview

RBAC - System Basics

There are three main concepts to be familiar with: Roles, Resources, and Users. Users can be members of a role, which gives them certain access to any resources associated with that role, or any resources associated with "descendent" roles.

For example, if I have an organization named "MyCompany" and I want to allow two people, "Alice", and "Bob", access to manage all of the settings associated with that organization, I'd make them both members of the organization's admin_role.

It is often the case that you have many Roles in a system, and you want some roles to include all of the capabilities of other roles. For example, you may want a System Administrator to have access to everything that an Organization Administrator has access to, who has everything that a Project Administrator has access to, and so on. We refer to this concept as the 'Role Hierarchy', and is represented by allowing roles to have "Parent Roles". Any permission that a role has is implicitly granted to any parent roles (or parents of those parents, and so on). Of course roles can have more than one parent, and capabilities are implicitly granted to all parents. (Technically speaking, this forms a directional acyclic graph instead of a strict hierarchy, but the concept should remain intuitive.)

Implementation Overview

The RBAC system allows you to create and layer roles for controlling access to resources. Any Django Model can be made into a resource in the RBAC system by using the ResourceMixin. Once a model is accessible as a resource, you can extend the model definition to have specific roles using the ImplicitRoleField. Within the declaration of this role field you can also specify any parents the role may have, and the RBAC system will take care of all of the appropriate ancestral binding that takes place behind the scenes to ensure that the model you've declared is kept up to date as the relations in your model change.

Roles

Roles are defined for a resource. If a role has any parents, these parents will be considered when determining what roles are checked when accessing a resource.

ResourceA
 |-- AdminRole

ResourceB
 | -- AdminRole
       |-- parent = ResourceA.AdminRole

When a user attempts to access ResourceB, we will check for their access using the set of all unique roles, including the parents.

ResourceA.AdminRole, ResourceB.AdminRole

This would provide any members of the above roles with access to ResourceB.

Singleton Role

There is a special case Singleton Role that you can create. This type of role is for system-wide roles.

Models

The RBAC system defines a few new models. These models represent the underlying RBAC implementation and generally will be abstracted away from your daily development tasks by the implicit fields and mixins.

Role

Role defines a single role within the RBAC implementation. It encapsulates the ancestors, parents, and members for a role. This model is intentionally kept dumb and it has no explicit knowledge of a Resource. The Role model (get it?), defines some methods that aid in the granting and creation of roles.

visible_roles(cls, user)

visible_roles is a class method that will look up all of the Role instances a user can "see". This includes any roles the user is a direct descendent of as well as any ancestor roles.

singleton(cls, name)

The singleton class method is a helper method on the Role model that helps in the creation of singleton roles. It will return the role by name if it already exists or create and return the new role in the case it does not.

get_absolute_url(self)

get_absolute_url returns the consumable URL endpoint for the Role.

rebuild_role_ancestor_list(self)

rebuild_role_ancestor_list will rebuild the current role ancestry that is stored in the ancestors field of a Role. This is called for you by save and different Django signals.

is_ancestor_of(self, role)

is_ancestor_of returns if the given role is an ancestor of the current Role instance.

user in role

You may use the user in some_role syntax to check and see if the specified user is a member of the given role, or a member of any ancestor role.

Fields

ImplicitRoleField

ImplicitRoleField fields are declared on your model. They provide the definition of grantable roles for accessing your resource. You may (and should) use the parent_role parameter to specify any parent roles that should inherit privileges implied by the role.

parent_role is the link to any parent roles you want considered when a user is requesting access to your resource. A parent_role can be declared as a single string, "parent.read_role", or a list of many roles, ['parentA.read_role', 'parentB.read_role'] which will make each listed role a parent. You can also use the syntax [('parentA.read_role', 'parentB.read_role'), 'parentC.read_role'] to make (parentA.read_role OR parentB.read_role) AND 'parentC.read_role parents (so parentB.read_role will be added only if parentA.read_role was None). If any listed role can't be evaluated (for example if there are None components in the path), then they are simply ignored until the value of the field changes.

Mixins

ResourceMixin

By mixing in the ResourceMixin to your model, you are turning your model in to a resource in the eyes of the RBAC implementation. Your model will gain the helper methods that aid in the checking the access a users roles provides them to your resource.

accessible_objects(cls, user, role_field)

accessible_objects is a class method to use instead of Model.objects. This method will restrict the query of objects to only those that the user has access to - specifically those objects which the user is a member of the specified role (either directly or indirectly).

    objects = MyModel.accessible_objects(user, 'admin_role')
    objects.filter(name__istartswith='december')

get_permissions(self, user)

get_permissions is an instance method that will give you the list of role names that the user has access to for a given object.

    >>> instance.get_permissions(admin)
    ['admin_role', 'execute_role', 'read_role']

Usage

After exploring the Overview, the usage of the RBAC implementation in your code should feel unobtrusive and natural.

    # make your model a Resource
    class Document(Model, ResourceMixin):
       ...
    # declare your new role
    readonly_role = ImplicitRoleField(
        role_name="readonly",
        permissions={'read':True},
    )

Now that your model is a resource and has a Role defined, you can begin to access the helper methods provided to you by the ResourceMixin for checking a user's access to your resource. Here is the output of a Python REPL session:

    # we've created some documents and a user
    >>> document = Document.objects.filter(pk=1)
    >>> user = User.objects.first()
    >>> user in document.read_role
    False  # not accessible by default
    >>> document.readonly_role.memebers.add(user)
    >>> user in document.read_role
    True   # now it is accessible
    >>> user in document.admin_role
    False  # my role does not have admin permission