logical-permissions 1.0.2

Provides support for dictionary-based permissions with logic gates such as AND and OR.

# logical-permissions

This is a generic library that provides support for dictionary-based
permissions with logic gates such as AND and OR. You can register any
kind of permission types such as roles and flags. The idea with this
library is to be an ultra-flexible foundation that can be used by any
framework. It supports python 2 and 3.

Getting started
---------------

Installation
~~~~~~~~~~~~

``pip install logical-permissions``

Usage
~~~~~

.. code:: python

# Simple example for checking user roles

from logical_permissions.LogicalPermissions import LogicalPermissions

lp = LogicalPermissions()

def roleCallback(role, context):
access = False
if 'roles' in context.get('user', {}):
access = role in context['user']['roles']
return access
lp.addType('role', roleCallback)

permissions = {
'role': ['editor', 'writer'],
}

user = {
'id': 1,
'roles': ['writer'],
}

access = lp.checkAccess(permissions, {'user': user})
print('Access granted: {0}'.format(access))

The main api method is
```LogicalPermissions::checkAccess()`` <#checkaccess>`__, which checks
the access for a **permission tree**. A permission tree is a bundle of
permissions that apply to a specific action. Let's say for example that
you want to restrict access for updating a user. You'd like only users
with the role "admin" to be able to update any user, but users should
also be able to update their own user data (or at least some of it).
With the structure this package provides, these conditions could be
expressed elegantly in a permission tree as such:

.. code:: python

{
'OR': {
'role': 'admin',
'flag': 'is_author',
},
}

In this example ``role`` and ``flag`` are the evaluated permission
types. For this example to work you will need to register the permission
types 'role' and 'flag' so that the class knows which callbacks are
responsible for evaluating the respective permission types. You can do
that with ```LogicalPermissions::addType()`` <#addtype>`__.

Bypassing permissions
~~~~~~~~~~~~~~~~~~~~~

This packages also supports rules for bypassing permissions completely
for superusers. In order to use this functionality you need to register
a callback with
```LogicalPermissions::setBypassCallback()`` <#setbypasscallback>`__.
The registered callback will run on every permission check and if it
returns ``True``, access will automatically be granted. If you want to
make exceptions you can do so by adding ``'no_bypass': True`` to the
first level of a permission tree. You can even use permissions as
conditions for ``no_bypass``.

Examples:

.. code:: python

# Disallow access bypassing
{
'no_bypass': True,
'role': 'editor',
}

.. code:: python

# Disallow access bypassing only if the user is an admin
{
'no_bypass': {
'role': 'admin',
},
'role': 'editor',
}

Logic gates
-----------

Currently supported logic gates are `AND <#and>`__, `NAND <#nand>`__,
`OR <#or>`__, `NOR <#nor>`__, `XOR <#xor>`__ and `NOT <#not>`__. You can
put logic gates anywhere in a permission tree and nest them to your
heart's content. All logic gates support a dictionary or list as their
value, except the NOT gate which has special rules. If a dictionary or
list of values does not have a logic gate as its key, an OR gate will be
assumed.

AND
~~~

A logic AND gate returns True if all of its children return True.
Otherwise it returns False.

Examples:

.. code:: python

# Allow access only if the user is both an editor and a sales person
{
'role': {
'AND': ['editor', 'sales'],
},
}

.. code:: python

# Allow access if the user is both a sales person and the author of the document
{
'AND': {
'role': 'sales',
'flag': 'is_author',
},
}

NAND
~~~~

A logic NAND gate returns True if one or more of its children returns
False. Otherwise it returns False.

Examples:

.. code:: python

# Allow access by anyone except if the user is both an editor and a sales person
{
'role': {
'NAND': ['editor', 'sales'],
},
}

.. code:: python

# Allow access by anyone, but not if the user is both a sales person and the author of the document.
{
'NAND': {
'role': 'sales',
'flag': 'is_author',
},
}

OR
~~

A logic OR gate returns True if one or more of its children returns
True. Otherwise it returns False.

Examples:

.. code:: python

# Allow access if the user is either an editor or a sales person, or both.
{
'role': {
'OR': ['editor', 'sales'],
},
}

.. code:: python

# Allow access if the user is either a sales person or the author of the document, or both
{
'OR': {
'role': 'sales',
'flag': 'is_author',
},
}

Shorthand OR
~~~~~~~~~~~~

As previously mentioned, any dictionary or list of values that doesn't
have a logic gate as its key is interpreted as belonging to an OR gate.

In other words, this permission tree:

.. code:: python

{
'role': ['editor', 'sales'],
}

is interpreted exactly the same way as this permission tree:

.. code:: python

{
'role': {
'OR': ['editor', 'sales'],
},
}

NOR
~~~

A logic NOR gate returns True if all of its children returns False.
Otherwise it returns False.

Examples:

.. code:: python

# Allow access if the user is neither an editor nor a sales person
{
'role': {
'NOR': ['editor', 'sales'],
},
}

.. code:: python

# Allow neither sales people nor the author of the document to access it
{
'NOR': {
'role': 'sales',
'flag': 'is_author',
},
}

XOR
~~~

A logic XOR gate returns True if one or more of its children returns
True and one or more of its children returns False. Otherwise it returns
False. An XOR gate requires a minimum of two elements in its value list
or dictionary.

Examples:

.. code:: python

# Allow access if the user is either an editor or a sales person, but not both
{
'role': {
'XOR': ['editor', 'sales'],
},
}

.. code:: python

# Allow either sales people or the author of the document to access it, but not if the user is both a sales person and the author
{
'XOR': {
'role': 'sales',
'flag': 'is_author',
},
}

NOT
~~~

A logic NOT gate returns True if its child returns False, and vice
versa. The NOT gate is special in that it supports either a string or a
dictionary with a single element as its value.

Examples:

.. code:: python

# Allow access for anyone except editors
{
'role': {
'NOT': 'editor',
},
}

.. code:: python

# Allow access for anyone except the author of the document
{
'NOT': {
'flag': 'is_author',
},
}

API Documentation
-----------------

Table of Contents
-----------------

- `LogicalPermissions <#logicalpermissions>`__

- `addType <#addtype>`__
- `removeType <#removetype>`__
- `typeExists <#typeexists>`__
- `getTypeCallback <#gettypecallback>`__
- `getTypes <#gettypes>`__
- `setTypes <#settypes>`__
- `getBypassCallback <#getbypasscallback>`__
- `setBypassCallback <#setbypasscallback>`__
- `checkAccess <#checkaccess>`__

LogicalPermissions
------------------

addType
~~~~~~~

Adds a permission type.

.. code:: python

LogicalPermissions::addType( name, callback )

**Parameters:**

+----------------+----------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Parameter | Type | Description |
+================+================+===========================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================+
| ``name`` | **string** | The name of the permission type. |
+----------------+----------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| ``callback`` | **callable** | The callback that evaluates the permission type. Upon calling checkAccess() the registered callback will be passed two parameters: a permission string (such as a role) and the context dictionary passed to checkAccess(). The permission will always be a single string even if for example multiple roles are accepted. In that case the callback will be called once for each role that is to be evaluated. The callback should return a boolean which determines whether access should be granted. |
+----------------+----------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

--------------

removeType
~~~~~~~~~~

Removes a permission type.

.. code:: python

LogicalPermissions::removeType( name )

**Parameters:**

+-------------+--------------+------------------------------------+
| Parameter | Type | Description |
+=============+==============+====================================+
| ``name`` | **string** | The name of the permission type. |
+-------------+--------------+------------------------------------+

--------------

typeExists
~~~~~~~~~~

Checks whether a permission type is registered.

.. code:: python

LogicalPermissions::typeExists( name )

**Parameters:**

+-------------+--------------+------------------------------------+
| Parameter | Type | Description |
+=============+==============+====================================+
| ``name`` | **string** | The name of the permission type. |
+-------------+--------------+------------------------------------+

**Return Value:**

True if the type is found or False if the type isn't found.

--------------

getTypeCallback
~~~~~~~~~~~~~~~

Gets the callback for a permission type.

.. code:: python

LogicalPermissions::getTypeCallback( name )

**Parameters:**

+-------------+--------------+------------------------------------+
| Parameter | Type | Description |
+=============+==============+====================================+
| ``name`` | **string** | The name of the permission type. |
+-------------+--------------+------------------------------------+

**Return Value:**

Callback for the permission type.

--------------

getTypes
~~~~~~~~

Gets all defined permission types.

.. code:: python

LogicalPermissions::getTypes( )

**Return Value:**

A dictionary of permission types with the structure {name: callback,
name2: callback2, ...}. This dictionary is shallow copied.

--------------

setTypes
~~~~~~~~

Overwrites all defined permission types.

.. code:: python

LogicalPermissions::setTypes( types )

**Parameters:**

+-------------+------------------+-----------------------------------------------------------------------------------------------------------------------------------+
| Parameter | Type | Description |
+=============+==================+===================================================================================================================================+
| ``types`` | **dictionary** | A dictionary of permission types with the structure {name: callback, name2: callback2, ...}. This dictionary is shallow copied. |
+-------------+------------------+-----------------------------------------------------------------------------------------------------------------------------------+

--------------

getBypassCallback
~~~~~~~~~~~~~~~~~

Gets the registered callback for access bypass evaluation.

.. code:: python

LogicalPermissions::getBypassCallback( )

**Return Value:**

Bypass access callback.

--------------

setBypassCallback
~~~~~~~~~~~~~~~~~

Sets the callback for access bypass evaluation.

.. code:: python

LogicalPermissions::setBypassCallback( callback )

**Parameters:**

+----------------+----------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Parameter | Type | Description |
+================+================+=======================================================================================================================================================================================================================================================================================+
| ``callback`` | **callable** | The callback that evaluates access bypassing. Upon calling checkAccess() the registered bypass callback will be passed one parameter, which is the context dictionary passed to checkAccess(). It should return a boolean which determines whether bypass access should be granted. |
+----------------+----------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

--------------

checkAccess
~~~~~~~~~~~

Checks access for a permission tree.

.. code:: python

LogicalPermissions::checkAccess( permissions, context )

**Parameters:**

+-------------------+------------------+----------------------------------------------------------------------------------------+
| Parameter | Type | Description |
+===================+==================+========================================================================================+
| ``permissions`` | **dictionary** | The permission tree to be evaluated. |
+-------------------+------------------+----------------------------------------------------------------------------------------+
| ``context`` | **dictionary** | A context dictionary that could for example contain the evaluated user and document. |
+-------------------+------------------+----------------------------------------------------------------------------------------+

**Return Value:**

True if access is granted or False if access is denied.

--------------