Package: policy
# PolicyA Policy library provides support for RBAC policy enforcement.## PrefaceWhen I used ``Flask`` to write a ``RESTful web service``, I didn't find a suitable extension to handle endpoints' permission control. Because I really like the permission control method of ``OpenStack`` services which based on a policy file. So I want to implement a more generic library similar to ``oslo.policy``.## Demo### Generate Policy FileSuppose there are two roles: **user** and **admin**, and two resources: **article** and **user**. We have 3 policies:- Only user can update article- Creating new user requires admin permission.- Only article owners or admin-role user can delete articles.Based on the previous description, we generate the following policy file ``policy.json``:{"is_admin": "role:admin","is_user": "role:user or role:admin","article:update": "rule:is_user","article:delete": "role:admin or id:%(user_id)s","user:create": "rule:is_admin"}### Enforce Policy With Flask ApplicationSuppose we have a simple ``Flask`` application which provides two api: creating new user and deleting article and we run it:```#!/usr/bin/env python# -*- coding: utf-8 -*-import functoolsfrom flask import Flask, request, gfrom policy import Enforcerfrom policy.exceptions import PolicyNotAuthorizedapp = Flask(__name__)enforcer = Enforcer('policy.json', raise_error=True)@app.errorhandler(PolicyNotAuthorized)def handle_policy_exception(error):return str(error)users = {'lily': {'id': 'd55a4192eb3b489589d5ee95dcf3af7d','roles': ['user', 'admin']},'kate': {'id': '1a535309687244e2aa434b25ef4bfb59','roles': ['user']},'lucy': {'id': '186977181e7f4a9e85104ca017e845f3','roles': ['user']}}articles = {'python': {'id': 'e6e31ad693734b269099d9acac2cb800','user_id': '1a535309687244e2aa434b25ef4bfb59'  # owned  by kate}}def login_required(func):@functools.wraps(func)def wrapped(*args, **kwargs):username = request.args.get('me')credential = users.get(username)if not credential:raise Exception('login required')else:g.cred = credentialreturn func(*args, **kwargs)return wrappeddef enforce_policy(rule):"""Enforce a policy to a API."""def wrapper(func):"""Decorator used for wrap API."""@functools.wraps(func)def wrapped(*args, **kwargs):if enforcer.enforce(rule, {}, g.cred):return func(*args, **kwargs)return wrappedreturn wrapper@app.route('/user', methods=['GET'])@login_required@enforce_policy('user:create')def create_user():# do create action herereturn 'user created'@app.route('/article', methods=['GET'])@login_requireddef delete_article():article_name = request.args.get('name')article = articles.get(article_name)# do fine-grained permission check hereenforcer.enforce('article:delete', article, g.cred)# do delete action herereturn 'arcticle %s deleted' % article['id']if __name__ == '__main__':app.run(port=8888, debug=True)```#### View-LevelWe provide a ``enforce_policy`` decorator to enforce policy on views ``create_user``.We head to http://127.0.0.1:8888/user?me=kate to simulate ``kate``'s creating user and get a error:user:create on {} by {'roles': ['user'], 'id': '1a535309687244e2aa434b25ef4bfb59'} disallowed by policyThen we head to http://127.0.0.1:8888/user?me=lily to simulate ``lily``'s creating user and get a successful response:user created#### Fine-GrainedIn some scenarios we want a fine-grained permission check. We enforce policy inside view ``delete_article``, because outside of it we can't know which article the user wants to delete.We head to http://127.0.0.1:8888/article?me=lucy&name=python to simulate ``lucy``'s deleting article and get a error:article:delete on {'user_id': '1a535309687244e2aa434b25ef4bfb59', 'id': 'e6e31ad693734b269099d9acac2cb800'} by {'roles': ['user'], 'id': '186977181e7f4a9e85104ca017e845f3'} disallowed by policyThen we head to http://127.0.0.1:8888/article?me=kate&name=python to simulate ``kate``'s deleting article and get a successful response because ``kate`` is the article's owner:arcticle e6e31ad693734b269099d9acac2cb800 deletedFinally we head to http://127.0.0.1:8888/article?me=lily&name=python to simulate ``lily``'s deleting article and get a successful response because ``lily`` is a admin-role user:arcticle e6e31ad693734b269099d9acac2cb800 deleted