permission 0.1.2

Simple permission control for Python Web Frameworks.

Simple and flexible permission control for Flask app.

Features

• Simple: all you need to do is subclassing Rule and Permission class.

• Flexible: support rule inheritance and bitwise operations(& and |) to build your own rules.

Installation

$ pip install permission

Rule and Permission

Rule has 3 methods which can be overrided:

• base(): define base rule.

• check(): determine whether this rule should be passed or not.

• deny(): will be executed when check() failed.

You should always override check() and deny() while overriding base() as needed.

Permission has 1 methods which can be overrided:

• rule(): define rules needed by this permission

You should always override rule().

Permission has 2 instance methods you can used in codes:

• check(): call this to check rules of this permission

• deny(): call this to execute codes when check() failed

Usage

First you need to define your own rules by subclassing Rule then override check() and deny():

# rules.py
from flask import session, abort, flash
from permission import Rule

class UserRule(Rule):
    def check(self):
        """Check if there is a user signed in."""
        return 'user_id' in session

    def deny(self):
        """When no user signed in, redirect to signin page."""
        flash('This action need the login')
        return redirect(url_for('signin'))

Then you define permissions by subclassing Permission and override rule():

# permissions.py
from permission import Permission
from .rules import UserRule

class UserPermission(Permission):
    """Only signin user has this permission."""
    def rule(self):
        return UserRule()

Use as view decorator:

from .permissions import UserPermission

@app.route('/settings')
@UserPermission()
def settings():
    """User settings page, only accessable for sign-in user."""
    return render_template('settings.html')

Use in view codes:

from .permissions import UserPermission

@app.route('/settions')
def settings():
    permission = UserPermission()
    if not permission.check()
        return permission.deny()
    return render_template('settings.html')

Use in Jinja2 templates, first you need to inject your defined permissions to template context:

from .permissions import UserPermission

@app.context_processor
def inject_vars():
    return dict(
        permissions=permissions
    )

Then in templates:

{% if permissions.UserPermission().check() %}
    <a href="{{ url_for('new') }}">New</a>
{% endif %}

Inheritance

Need to say, inheritance here is not the same thing as Python class inheritance, it’s just means you can use RuleA as the base rule of RuleB.

We achieve this by overriding base().

Examples

Let’s say an administrator user should always be a user:

# rules.py
from flask import session, abort, flash
from permission import Rule


class UserRule(Rule):
    def check(self):
        return 'user_id' in session

    def deny(self):
        flash('This action need the login')
        return redirect(url_for('signin'))


class AdminRule(Rule):
    def base(self):
        return UserRule()

    def check(self):
        user_id = int(session['user_id'])
        user = User.query.filter(User.id == user_id).first()
        return user and user.is_admin

    def deny(self):
        abort(403)

Bitwise operations

• RuleA & RuleB means it will be passed when both RuleA and RuleB are passed.

• RuleA | RuleB means it will be passed either RuleA or RuleB is passed.

Examples

Let’s say we need to build a forum with Flask. Only the topic creator and administrator user can edit a topic:

First let’s define rules:

# rules.py
from flask import session, abort, flash
from permission import Rule
from .models import User, Topic


class UserRule(Rule):
    def check(self):
        """Check if there is a user signed in."""
        return 'user_id' in session

    def deny(self):
        """When no user signed in, redirect to signin page."""
        flash('This action need the login')
        return redirect(url_for('signin'))


class AdminRule(Rule):
    def base(self):
        return UserRule()

    def check(self):
        user_id = int(session['user_id'])
        user = User.query.filter(User.id == user_id).first()
        return user and user.is_admin

    def deny(self):
        abort(403)


class TopicCreatorRule(Rule):
    def __init__(self, topic_id):
        self.topic_id = topic_id
        super(TopicCreatorRule, self).__init__()

    def base(self):
        return UserRule()

    def check(self):
        topic = Topic.query.filter(Topic.id == self.topic_id).first()
        return topic and topic.user_id == session['user_id']

    def deny(self):
        abort(403)

Then define permissions:

# permissions.py
from permission import Permission


class UserPermission(Permission):
    def rule(self):
        return UserRule()


class AdminPermission(Permission):
    def rule(self):
        return AdminRule()


class TopicAdminPermission(Permission):
    def __init__(self, topic_id):
        self.topic_id = topic_id
        super(TopicAdminPermission, self).__init__()

    def rule(self):
        return AdminRule() | QuestionOwnerRule(self.topic_id)

So we can use TopicAdminPermission in edit_topic view:

from .permissions import TopicAdminPermission

@app.route('topic/<int:topic_id>/edit')
def edit_topic(topic_id):
    topic = Topic.query.get_or_404(topic_id)
    permission = TopicAdminPermission(topic_id)
    if not permission.check():
        return permission.deny()
    ...