Removed deprecated CsrfResponseMiddleware, and corresponding tests and docs

"""

import hashlib

import itertools

import re

import random

from django.utils.cache import patch_vary_headers

from django.utils.http import same_origin

from django.utils.log import getLogger

from django.utils.safestring import mark_safe

from django.utils.crypto import constant_time_compare

_POST_FORM_RE = \

    re.compile(r'(<form\W[^>]*\bmethod\s*=\s*(\'|"|)POST(\'|"|)\b[^>]*>)', re.IGNORECASE)

_HTML_TYPES = ('text/html', 'application/xhtml+xml')

logger = getLogger('django.request')

# Use the system (hardware-based) random number generator if it exists.

    return hashlib.md5("%s%s" % (randrange(0, _MAX_CSRF_KEY), settings.SECRET_KEY)).hexdigest()

def _make_legacy_session_token(session_id):

    return hashlib.md5(settings.SECRET_KEY + session_id).hexdigest()

def get_token(request):

    """

    Returns the the CSRF token required for a POST form. The token is an

        patch_vary_headers(response, ('Cookie',))

        response.csrf_processing_done = True

        return response

class CsrfResponseMiddleware(object):

    """

    DEPRECATED

    Middleware that post-processes a response to add a csrfmiddlewaretoken.

    This exists for backwards compatibility and as an interim measure until

    applications are converted to using use the csrf_token template tag

    instead. It will be removed in Django 1.4.

    """

    def __init__(self):

        import warnings

        warnings.warn(

            "CsrfResponseMiddleware and CsrfMiddleware are deprecated; use CsrfViewMiddleware and the template tag instead (see CSRF documentation).",

            DeprecationWarning

        )

    def process_response(self, request, response):

        if getattr(response, 'csrf_exempt', False):

            return response

        if response['Content-Type'].split(';')[0] in _HTML_TYPES:

            csrf_token = get_token(request)

            # If csrf_token is None, we have no token for this request, which probably

            # means that this is a response from a request middleware.

            if csrf_token is None:

                return response

            # ensure we don't add the 'id' attribute twice (HTML validity)

            idattributes = itertools.chain(("id='csrfmiddlewaretoken'",),

                                           itertools.repeat(''))

            def add_csrf_field(match):

                """Returns the matched <form> tag plus the added <input> element"""

                return mark_safe(match.group() + "<div style='display:none;'>" + \

                "<input type='hidden' " + idattributes.next() + \

                " name='csrfmiddlewaretoken' value='" + csrf_token + \

                "' /></div>")

            # Modify any POST forms

            response.content, n = _POST_FORM_RE.subn(add_csrf_field, response.content)

            if n > 0:

                # Content varies with the CSRF cookie, so set the Vary header.

                patch_vary_headers(response, ('Cookie',))

                # Since the content has been modified, any Etag will now be

                # incorrect.  We could recalculate, but only if we assume that

                # the Etag was set by CommonMiddleware. The safest thing is just

                # to delete. See bug #9163

                del response['ETag']

        return response

class CsrfMiddleware(object):

    """

    Django middleware that adds protection against Cross Site

    Request Forgeries by adding hidden form fields to POST forms and

    checking requests for the correct value.

    CsrfMiddleware uses two middleware, CsrfViewMiddleware and

    CsrfResponseMiddleware, which can be used independently.  It is recommended

    to use only CsrfViewMiddleware and use the csrf_token template tag in

    templates for inserting the token.

    """

    # We can't just inherit from CsrfViewMiddleware and CsrfResponseMiddleware

    # because both have process_response methods.

    def __init__(self):

        self.response_middleware = CsrfResponseMiddleware()

        self.view_middleware = CsrfViewMiddleware()

    def process_response(self, request, resp):

        # We must do the response post-processing first, because that calls

        # get_token(), which triggers a flag saying that the CSRF cookie needs

        # to be sent (done in CsrfViewMiddleware.process_response)

        resp2 = self.response_middleware.process_response(request, resp)

        return self.view_middleware.process_response(request, resp2)

    def process_view(self, request, callback, callback_args, callback_kwargs):

        return self.view_middleware.process_view(request, callback, callback_args,

                                                 callback_kwargs)

side-effect free.  POST requests can then be protected by following the steps

below.

.. versionadded:: 1.2

    The 'contrib' apps, including the admin, use the functionality described

    here. Because it is security related, a few things have been added to core

    functionality to allow this to happen without any required upgrade steps.

.. _Cross Site Request Forgeries: http://www.squarefree.com/securitytips/web-developers.html#CSRF

How to use it

=============

.. versionchanged:: 1.2

    The template tag functionality (the recommended way to use this) was added

    in version 1.2. The previous method (still available) is described under

    `Legacy method`_.

To enable CSRF protection for your views, follow these steps:

    1. Add the middleware

       ``'django.middleware.csrf.CsrfViewMiddleware'`` to your list of

       middleware classes, :setting:`MIDDLEWARE_CLASSES`.  (It should come

       before ``CsrfResponseMiddleware`` if that is being used, and before any

       view middleware that assume that CSRF attacks have been dealt with.)

       and before any view middleware that assume that CSRF attacks have

       been dealt with.)

       Alternatively, you can use the decorator

       ``django.views.decorators.csrf.csrf_protect`` on particular views you

    2. In any template that uses a POST form, use the :ttag:`csrf_token` tag inside

       the ``<form>`` element if the form is for an internal URL, e.g.::

           <form action="" method="post">{% csrf_token %}

           <form action="." method="post">{% csrf_token %}

       This should not be done for POST forms that target external URLs, since

       that would cause the CSRF token to be leaked, leading to a vulnerability.

          takes care of this step for you.

The utility script ``extras/csrf_migration_helper.py`` can help to automate the

finding of code and templates that may need to be upgraded.  It contains full

help on how to use it.

finding of code and templates that may need these steps. It contains full help

on how to use it.

.. _csrf-ajax:

use it, you will have a security hole.  The 'belt and braces' strategy of using

both is fine, and will incur minimal overhead.

Legacy method

-------------

In Django 1.1, the template tag did not exist.  Instead, a post-processing

middleware that re-wrote POST forms to include the CSRF token was used.  If you

are upgrading a site from version 1.1 or earlier, please read this section and

the `Upgrading notes`_ below.  The post-processing middleware is still available

as ``CsrfResponseMiddleware``, and it can be used by following these steps:

    1. Follow step 1 above to install ``CsrfViewMiddleware``.

    2. Add ``'django.middleware.csrf.CsrfResponseMiddleware'`` to your

       :setting:`MIDDLEWARE_CLASSES` setting.

       ``CsrfResponseMiddleware`` needs to process the response before things

       like compression or setting ofETags happen to the response, so it must

       come after ``GZipMiddleware``, ``CommonMiddleware`` and

       ``ConditionalGetMiddleware`` in the list. It also must come after

       ``CsrfViewMiddleware``.

Use of the ``CsrfResponseMiddleware`` is not recommended because of the

performance hit it imposes, and because of a potential security problem (see

below).  It can be used as an interim measure until applications have been

updated to use the :ttag:`csrf_token` tag.  It is deprecated and will be

removed in Django 1.4.

Django 1.1 and earlier provided a single ``CsrfMiddleware`` class.  This is also

still available for backwards compatibility.  It combines the functions of the

two middleware.

Note also that previous versions of these classes depended on the sessions

framework, but this dependency has now been removed, with backward compatibility

support so that upgrading will not produce any issues.

Security of legacy method

~~~~~~~~~~~~~~~~~~~~~~~~~

The post-processing ``CsrfResponseMiddleware`` adds the CSRF token to all POST

forms (unless the view has been decorated with ``csrf_response_exempt``).  If

the POST form has an external untrusted site as its target, rather than an

internal page, that site will be sent the CSRF token when the form is submitted.

Armed with this leaked information, that site will then be able to successfully

launch a CSRF attack on your site against that user.  The

``@csrf_response_exempt`` decorator can be used to fix this, but only if the

page doesn't also contain internal forms that require the token.

.. _ref-csrf-upgrading-notes:

Upgrading notes

---------------

When upgrading to version 1.2 or later, you may have applications that rely on

the old post-processing functionality for CSRF protection, or you may not have

enabled any CSRF protection.  This section outlines the steps necessary for a

smooth upgrade, without having to fix all the applications to use the new

template tag method immediately.

First of all, the location of the middleware and related functions have

changed.  There are backwards compatible stub files so that old imports will

continue to work for now, but they are deprecated and will be removed in Django

1.4.  The following changes have been made:

 * Middleware have been moved to ``django.middleware.csrf``

 * Decorators have been moved to ``django.views.decorators.csrf``

======================================================  ==============================================

   Old                                                       New

======================================================  ==============================================

django.contrib.csrf.middleware.CsrfMiddleware           django.middleware.csrf.CsrfMiddleware

django.contrib.csrf.middleware.CsrfViewMiddleware       django.middleware.csrf.CsrfViewMiddleware

django.contrib.csrf.middleware.CsrfResponseMiddleware   django.middleware.csrf.CsrfResponseMiddleware

django.contrib.csrf.middleware.csrf_exempt              django.views.decorators.csrf.csrf_exempt

django.contrib.csrf.middleware.csrf_view_exempt         django.views.decorators.csrf.csrf_view_exempt

django.contrib.csrf.middleware.csrf_response_exempt     django.views.decorators.csrf.csrf_response_exempt

======================================================  ==============================================

You should update any imports, and also the paths in your

:setting:`MIDDLEWARE_CLASSES`.

If you have ``CsrfMiddleware`` in your :setting:`MIDDLEWARE_CLASSES`, you will now

have a working installation with CSRF protection.  It is recommended at this

point that you replace ``CsrfMiddleware`` with its two components,

``CsrfViewMiddleware`` and ``CsrfResponseMiddleware`` (in that order).

If you do not have any of the middleware in your :setting:`MIDDLEWARE_CLASSES`,

you will have a working installation but without any CSRF protection for your

views (just as you had before). It is strongly recommended to install

``CsrfViewMiddleware`` and ``CsrfResponseMiddleware``, as described above.

Note that contrib apps, such as the admin, have been updated to use the

``csrf_protect`` decorator, so that they are secured even if you do not add the

``CsrfViewMiddleware`` to your settings.  However, if you have supplied

customised templates to any of the view functions of contrib apps (whether

explicitly via a keyword argument, or by overriding built-in templates), **you

MUST update them** to include the :ttag:`csrf_token` template tag as described

above, or they will stop working.  (If you cannot update these templates for

some reason, you will be forced to use ``CsrfResponseMiddleware`` for these

views to continue working).

Note also, if you are using the comments app, and you are not going to add

``CsrfViewMiddleware`` to your settings (not recommended), you will need to add

the ``csrf_protect`` decorator to any views that include the comment forms and

target the comment views (usually using the :ttag:`comment_form_target` template

tag).

Assuming you have followed the above, all views in your Django site will now be

protected by the ``CsrfViewMiddleware``.  Contrib apps meet the requirements

imposed by the ``CsrfViewMiddleware`` using the template tag, and other

applications in your project will meet its requirements by virtue of the

``CsrfResponseMiddleware``.

The next step is to update all your applications to use the template tag, as

described in `How to use it`_, steps 2-3.  This can be done as soon as is

practical. Any applications that are updated will now require Django 1.1.2 or

later, since they will use the CSRF template tag which was not available in

earlier versions. (The template tag in 1.1.2 is actually a no-op that exists

solely to ease the transition to 1.2 — it allows apps to be created that have

CSRF protection under 1.2 without requiring users of the apps to upgrade to the

Django 1.2.X series).

The utility script ``extras/csrf_migration_helper.py`` can help to automate the

finding of code and templates that may need to be upgraded.  It contains full

help on how to use it.

Finally, once all applications are upgraded, ``CsrfResponseMiddleware`` can be

removed from your settings.

While ``CsrfResponseMiddleware`` is still in use, the ``csrf_response_exempt``

decorator, described in `Exceptions`_, may be useful.  The post-processing

middleware imposes a performance hit and a potential vulnerability, and any

views that have been upgraded to use the new template tag method no longer need

it.

Exceptions

----------

.. versionchanged:: 1.2

    Import paths for the decorators below were changed.

To manually exclude a view function from being handled by either of the two CSRF

middleware, you can use the ``csrf_exempt`` decorator, found in the

``django.views.decorators.csrf`` module. For example::

    def my_view(request):

        return HttpResponse('Hello world')

Like the middleware, the ``csrf_exempt`` decorator is composed of two parts: a

``csrf_view_exempt`` decorator and a ``csrf_response_exempt`` decorator, found

in the same module.  These disable the view protection mechanism

(``CsrfViewMiddleware``) and the response post-processing

(``CsrfResponseMiddleware``) respectively.  They can be used individually if

required.

Subdomains

----------

   outgoing POST forms.  The value of this field is the value of the CSRF

   cookie.

   This part is done by the template tag (and with the legacy method, it is done

   by ``CsrfResponseMiddleware``).

   This part is done by the template tag.

3. For all incoming POST requests, a CSRF cookie must be present, and the

   'csrfmiddlewaretoken' field must be present and correct. If it isn't, the

(see `9.1.1 Safe Methods, HTTP 1.1, RFC 2616`_), and so a CSRF attack with a GET

request ought to be harmless.

``CsrfResponseMiddleware`` checks the Content-Type before modifying the

response, and only pages that are served as 'text/html' or

'application/xml+xhtml' are modified.

.. _9.1.1 Safe Methods, HTTP 1.1, RFC 2616: http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html

Caching

=======

If the :ttag:`csrf_token` template tag is used by a template (or the ``get_token``

function is called some other way), ``CsrfViewMiddleware`` will add a cookie and

a ``Vary: Cookie`` header to the response.  Similarly,

``CsrfResponseMiddleware`` will send the ``Vary: Cookie`` header if it inserted

a token.  This means that these middleware will play well with the cache

middleware if it is used as instructed (``UpdateCacheMiddleware`` goes before

all other middleware).

If the :ttag:`csrf_token` template tag is used by a template (or the

``get_token`` function is called some other way), ``CsrfViewMiddleware`` will

add a cookie and a ``Vary: Cookie`` header to the response. This means that the

middleware will play well with the cache middleware if it is used as instructed

(``UpdateCacheMiddleware`` goes before all other middleware).

However, if you use cache decorators on individual views, the CSRF middleware

will not yet have been able to set the Vary header.  In this case, on any views

such as session fixation, that make giving subdomains to untrusted parties a bad

idea, and these vulnerabilities cannot easily be fixed with current browsers.

If you are using ``CsrfResponseMiddleware`` and your app creates HTML pages and

forms in some unusual way, (e.g.  it sends fragments of HTML in JavaScript

document.write statements) you might bypass the filter that adds the hidden

field to the form, in which case form submission will always fail.  You should

use the template tag or :meth:`django.middleware.csrf.get_token` to get

the CSRF token and ensure it is included when your form is submitted.

Contrib and reusable apps

=========================