django-session-csrf

What is this?

django-session-csrf is an alternative implementation of Django's CSRF protection that does not use cookies. Instead, it maintains the CSRF token on the server using Django's session backend. The csrf token must still be included in all POST requests (either with csrfmiddlewaretoken in the form or with the X-CSRFTOKEN header).

Installation

From PyPI::

pip install django-session-csrf

From github::

git clone git://github.com/mozilla/django-session-csrf.git

Replace django.core.context_processors.csrf with session_csrf.context_processor in your TEMPLATE_CONTEXT_PROCESSORS::

TEMPLATE_CONTEXT_PROCESSORS = (
    ...
    'session_csrf.context_processor',
    ...
)

Replace django.middleware.csrf.CsrfViewMiddleware with session_csrf.CsrfMiddleware in your MIDDLEWARE_CLASSES and make sure it is listed after the AuthenticationMiddleware::

MIDDLEWARE_CLASSES = (
    ...
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    ...
    'session_csrf.CsrfMiddleware',
    ...
)

Then we have to monkeypatch Django to fix the @csrf_protect decorator::

import session_csrf
session_csrf.monkeypatch()

Make sure that's in something like your root urls.py so the patch gets applied before your views are imported.

Differences from Django

django-session-csrf does not assign CSRF tokens to anonymous users because we don't want to support a session for every anonymous user. Instead, views that need anonymous forms can be decorated with @anonymous_csrf::

from session_csrf import anonymous_csrf

@anonymous_csrf
def login(request):
    ...

anonymous_csrf uses the cache to give anonymous users a lightweight session. It sends a cookie to uniquely identify the user and stores the CSRF token in the cache. It can be controlled through these settings:

``ANON_COOKIE``
    the name used for the anonymous user's cookie

    Default: ``anoncsrf``

``ANON_TIMEOUT``
    the cache timeout (in seconds) to use for the anonymous CSRF tokens

    Default: ``60 * 60 * 2  # 2 hours``

Note that by default Django uses local-memory caching, which will not work with anonymous CSRF if there is more than one web server thread. To use anonymous CSRF, you must configure a cache that's shared between web server instances, such as Memcached. See the Django cache documentation <https://docs.djangoproject.com/en/dev/topics/cache/>_ for more information.

If you only want a view to have CSRF protection for logged-in users, you can use the anonymous_csrf_exempt decorator. This could be useful if the anonymous view is protected through a CAPTCHA, for example.

::

from session_csrf import anonymous_csrf_exempt

@anonymous_csrf_exempt
def protected_in_another_way(request):
    ...

If you want all views to have CSRF protection for anonymous users, use the following setting:

``ANON_ALWAYS``
    always provide CSRF protection for anonymous users

    Default: False

Why do I want this?

• Your site is on a subdomain with other sites that are not under your control, so cookies could come from anywhere.
• You're worried about attackers using Flash to forge HTTP headers.
• You're tired of requiring a Referer header.

Why don't I want this?

• Storing tokens in sessions means you have to hit your session store more often.
• It's a little bit more work to CSRF-protect forms for anonymous users.