# 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

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`. This role field allows you to
configure the name of a role, any parents a role may have, and the permissions having this role will grant you to the resource.

### Roles

Roles are defined for a resource. If a role has any parents, these parents will be considered when determing
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, include the parents.

    set: ResourceA.AdminRole, ResourceB.AdminRole

This would provide anyone with the above roles 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 implemnentation 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 `parents` and `members` for a role. This model is intentially kepts 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.

##### `grant(self, resource, permissions)`

The `grant` instance method takes a resource and a set of permissions (see below) and creates an entry in the `RolePermission` table (described below). The result of this being that any member of this role will now have those granted permissions to the resource. The `grant` method considers a resource to be anything that is explicitly of the `Resource` type or any model that has a `resource` field that is of type `Resource`.

##### `singleton(name)`

The `singleton` static 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 it in the case it does not.

##### `rebuild_role_hierarchy_cache(self)`

`rebuild_role_hierarchy` will rebuild the current role hierarchy that is stored in the `RoleHierarchy` table. This speeds up the querying of parent roles when assembling a users set of roles. This method is called for you automatically during `save`.

#### `Resource`

#### `RoleHierarchy`

#### `RolePermission`

### Fields

#### `ImplicitRoleField`

`ImplicitRoleField` role fields are defined on your model. They provide the definition of grantable roles for accessing your 
`Resource`. Configuring the role is done using some keyword arguments that are provided during declaration.

`resource_field` is the name of the field in your model that is a `ForeignKey` to a `Resource`. If you use the 'ResourceMixin', this field is added to your model for you and is called `resource`. This field is required for the RBAC implementation to integrate any of the role fields you declare for your model. If you did not use the `ResourceMixin` and you have manually added a `Resource` link to your model you will need to set this field accordingly.

`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.readonly`, or a list of many roles, `['parentA.readonly', 'parentB.readonly']`. It is important to note that a user does not need a parent role to access a resource if granted the role for that resource explicitly. Also a user will not have access to any parent resources by being granted a role for a child resource. We demonstrate this in the _Usage_ section of this document.

`role_name` is the display name of the role. This is useful when generating reports or looking the results of queries.

`permissions` is a dictionary of set permissions that a user with this role will gain to your `Resource`. A permission defaults to `False` if not explicitly provided. Below is a list of available permissions. The special permission `all` is a shortcut for generating a dict with all of the explicit permissions listed below set to `True`.

```python
    # Available Permissions
    {'create':True, 'read':True, 'write':True, 'update':True,
     'delete':True, 'scm_update':True, 'use':True, 'execute':True}
    # Special Permissions
    {'all':True}
    # Example: readonly
    {'read':True}
```

#### `ImplicitResourceField`

### 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. What this means simply is that your model will now have an `ImplicitResourceField` named resource. Your model will also gain some methods that aid in the checking the access a users roles provides them to a resource.

##### `accessible_objects(cls, user, permissions)`

`accessible_objects` is a class method to use instead of `Model.objects`. This method will restrict the query of objects to only the objects that a user has the passed in permissions for. This is useful when you want to only filter and display a `Resource` that a users role grants them the `permissions` to. Note that any permission fields that are left blank will default to `False`. `accessible_objects` will only filter out resources where the expected permission was `True` but was returned as `False`.

```python
    objects = Model.accessible_objects(user, {'write':True})
    objects.filter(name__istartswith='december')
```

##### `get_permissions(self, user)`

`get_permissions` is an instance method that will give you the permission dictionary for a given user. This permission dictionary will take in to account any parent roles the user is apart of.

```python
    >>> instance.get_permissions(admin)
    {'create':True, 'read':True, 'write':True, 'update':True,
     'delete':True, 'scm_update':True, 'execute':True, 'use':True}
```


##### `accessible_by(self, user, permissions)`

`accessible_by` is an instance method that wraps the `get_permissions` method. Given a user and a dictionary of permissions this method will return True or False if a users roles give them a set of permissions that match the provided permissions dict. Not that any permission fields left blank will default to `False`. `accessible_by` will only return `False` in a case where the passed in permission is expected to be `True` but was returned as `False`.

```python
    >>> instance.accessible_by(admin, {'use':True, 'read':True})
    True
```
## Usage

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

```python
    # make your model a Resource
    class Document(Model, ResourceMixin):
       ...
    # declare your new role
    readonly_role = ImplicitRoleField(
        role_name="readonly",
        resource_field="resource",
        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 users access to your resource. Here is the output of a Python REPL session.

```python
    # we've created some documents and a user
    >>> document = Document.objects.filter(pk=1)
    >>> user = User.objects.first()
    >>> document.accessible_by(user, {'read': True})
    False  # not accessible by default
    >>> document.readonly_role.memebers.add(user)
    >>> document.accessible_by(user, {'read':True})
    True   # now it is accessible
    >>> document.accessible_by(user, {'read':True, 'write':True})
    False  # my role does not have write permission
```