A simple role based access control utility for Python.
Python
Latest commit 0324c1f Mar 29, 2016 @shonenada shonenada Merge pull request #5 from dbaneman/preserve-role-evaluation-order-an…
…d-add-short-circuiting

Preserve role evaluation order and add short circuiting

README.rst

Simple RBAC

This is a simple role based access control utility in Python.

Quick Start

1. Install Simple RBAC

pip install simple-rbac

2. Create a Access Control List

import rbac.acl

acl = rbac.acl.Registry()

3. Register Roles and Resources

acl.add_role("member")
acl.add_role("student", ["member"])
acl.add_role("teacher", ["member"])
acl.add_role("junior-student", ["student"])

acl.add_resource("course")
acl.add_resource("senior-course", ["course"])

4. Add Rules

acl.allow("member", "view", "course")
acl.allow("student", "learn", "course")
acl.allow("teacher", "teach", "course")
acl.deny("junior-student", "learn", "senior-course")

5. Use It to Check Permission

if acl.is_allowed("student", "view", "course"):
    print("Students chould view courses.")
else:
    print("Students chould not view courses.")

if acl.is_allowed("junior-student", "learn", "senior-course"):
    print("Junior students chould learn senior courses.")
else:
    print("Junior students chould not learn senior courses.")

Custom Role and Resource Class

It’s not necessary to use string as role object and resource object like "Quick Start". You could define role class and resource class of yourself, such as a database mapped model in SQLAlchemy.

Whatever which role class and resource class you will use, it must implement __hash__ method and __eq__ method to be hashable.

Example

class Role(db.Model):
    """The role."""

    id = db.Column(db.Integer, primary_key=True)
    screen_name = db.Column(db.Unicode, nullable=False, unique=True)

    def __hash__(self):
        return hash("ROLE::%d" % self.id)

    def __eq__(self, other):
        return self.id == other.id


class Resource(db.Model):
    """The resource."""

    id = db.Column(db.Integer, primary_key=True)
    screen_name = db.Column(db.Unicode, nullable=False, unique=True)

    def __hash__(self):
        return hash("RESOURCE::%d" % self.id)

    def __eq__(self, other):
        return self.id == other.id

Of course, You could use the built-in hashable types too, such as tuple, namedtuple, frozenset and more.

Use the Identity Context Check Your Permission

Obviously, the work of checking permission is a cross-cutting concern. The module named rbac.context, our IdentityContext, provide some ways to make our work neater.

1. Create the Context Manager

acl = Registry()
context = IdentityContext(acl)

2. Set a Loader

The loader should load the roles of current user.

from myapp import get_current_user

@context.set_roles_loader
def second_load_roles():
    user = get_current_user()
    yield "everyone"
    for role in user.roles:
        yield str(role)

3. Protect Your Action

Now you could protect your action from unauthorized access. As you please, you could choose many ways to check the permission, including python decorator, python with statement or simple method calling.

Decorator

@context.check_permission("view", "article", message="can't view")
def article_page():
    return "your-article"

With Statement

def article_page():
    with context.check_permission("view", "article", message="can't view"):
        return "your-article"

Simple Method Calling

def article_page():
    context.check_permission("view", "article", message="can't view").check()
    return "your-article"

Exception Handler and Non-Zero Checking

Whatever which way you choosen, a exception rbac.context.PermissionDenied will be raised while a unauthorized access happening. The keyword arguments sent to the context.check_permission will be set into a attirbute named kwargs of the exception. You could get those data in your exception handler.

@context.check_permission("view", "article", message="can not view")
def article_page():
    return "your-article"

try:
    print article_page()
except PermissionDenied as exception:
    print "The access has been denied, you %s" % exception.kwargs['message']

If you don’t want to raise the exception but only check the access is allowed or not, you could use the checking like a boolean value.

if not context.check_permission("view", "article"):
    print "Oh! the access has been denied."

is_allowed = bool(context.check_permission("view", "article"))