permission 0.2.1

Simple and flexible permission control for Flask app.

Simple and flexible permission control for Flask app.

Features

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

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

Installation

$ pip install permission

Role

Role has 3 methods which can be overrided:

• base(): define base role.

• check(): determine whether this role 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

Permission has 1 method which can be overrided:

• role(): define role needed by this permission

You should always override role().

Permission has 2 instance methods you can use in codes:

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

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

Usage

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

# roles.py
from flask import session, flash, redirect, url_for
from permission import Role


class UserRole(Role):
    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('Sign in first.')
        return redirect(url_for('signin'))

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

# permissions.py
from permission import Permission
from .roles import UserRole


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

There are 3 ways to use the UserPermission defined above:

1. 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')

2. 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')

3. Use in Jinja2 templates

First you need to inject your defined permissions to template context:

from . import permissions


@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 %}

Role Inheritance

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

We achieve this by overriding base().

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

# roles.py
from flask import session, abort, flash, redirect, url_for
from permission import Role


class UserRole(Role):
    def check(self):
        return 'user_id' in session

    def deny(self):
        flash('Sign in first.')
        return redirect(url_for('signin'))


class AdminRole(Role):
    def base(self):
        return UserRole()

    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)

Role Bitwise Operations

• RoleA & RoleB means it will be passed when both RoleA and RoleB are passed.

• RoleA | RoleB means it will be passed either RoleA or RoleB is passed.

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

First define roles:

# roles.py
from flask import session, abort, flash, redirect, url_for
from permission import Role
from .models import User, Topic


class UserRole(Role):
    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('Sign in first.')
        return redirect(url_for('signin'))


class AdminRole(Role):
    def base(self):
        return UserRole()

    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 TopicCreatorRole(Role):
    def __init__(self, topic_id):
        self.topic_id = topic_id
        super(TopicCreatorRole, self).__init__()

    def base(self):
        return UserRole()

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

    def role(self):
        return AdminRole() | TopicCreatorRole(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()
    ...