flask-cookie-decode 0.3.0

flask-cookie-decode
###################

.. image:: https://travis-ci.com/wgwz/flask-cookie-decode.svg?branch=master
:target: https://travis-ci.com/wgwz/flask-cookie-decode

.. contents::

.. section-numbering::

Purpose
=======

Adds a ``cookie`` command to the built-in Flask CLI which will provide various
tools for debugging the secure session cookie that Flask uses by default.

Current available commands
--------------------------

1. `flask cookie decode`: decodes and verifies the signature of the session cookie

Background
==========

By default the Flask session uses a signed cookie to store its data. The Flask
application signs the cookie using its ``SECRET_KEY``. This provides the Flask
application a way to detect any tampering to the session data. If the application
is indeed using a secret key and secure hashing algorithm, the session signature
will be unique to application.

For more on the topic of the Flask session see these references:

* `How Secure Is The Flask User Session?`_
* `Quickstart for Flask Sessions`_
* `API Docs for Flask Sessions`_

.. _`How Secure Is The Flask User Session?`: https://blog.miguelgrinberg.com/post/how-secure-is-the-flask-user-session
.. _`Quickstart for Flask Sessions`: http://flask.pocoo.org/docs/1.0/quickstart/#sessions
.. _`API Docs for Flask Sessions`: http://flask.pocoo.org/docs/1.0/api/#sessions

Disclaimer: Keep your SECRET_KEY, secret!
-----------------------------------------

If you expose this key your application becomes vulnerable to session replay
attacks. `Here is an example`_ where an application exposed the ``SECRET_KEY``
during 404 errors. The example also illustrates how session replay works.

By default Flask does not expose the ``SECRET_KEY`` anywhere. It is up to you
the developer to keep it that way!

.. _`Here is an example`: https://terryvogelsang.tech/MITRECTF2018-my-flask-app/

Usage
=====

Installation
------------

.. code-block:: bash

$ pip install flask-cookie-decode

Extracting the cookie using browser tools
-----------------------------------------

.. image:: https://raw.githubusercontent.com/wgwz/flask-cookie-decode/master/docs/cookie.png
:alt: Finding the cookie in browser tools
:width: 100%
:align: center

Example Flask app
-----------------

See `examples/app.py <https://github.com/wgwz/flask-cookie-decode/blob/master/examples/app.py>`_:

.. code-block:: python

from flask import Flask, jsonify, session, request
from flask_cookie_decode import CookieDecode

app = Flask(__name__)
app.config.update({'SECRET_KEY': 'jlghasdghasdhgahsdg'})
cookie = CookieDecode()
cookie.init_app(app)

@app.route('/')
def index():
a = request.args.get('a')
session['a'] = a
return jsonify(dict(session))

Examples using the CLI:
-----------------------

1. A cookie with a valid signature:

.. code-block:: bash

$ export FLASK_APP=app.py
$ flask cookie decode eyJhIjoiYXNkYXNkamtqYXNkIn0.XCkk1Q.tTPu2Zhvn9KxgkP35ERAgyd8MzA
TrustedCookie(contents={'a': 'asdasdjkjasd'}, expiration='2019-01-30T20:04:37')

2. A cookie with an invalid signature:

.. code-block:: bash

$ export FLASK_APP=app.py
$ flask cookie decode eyJhIjoiYXNkYXNkamtqYXNkIn0.XCkk1Q.tTPu2Zhvn9KxgkP35ERAgyd8MzA
UntrustedCookie(contents={'a': 'asdasdjkjasd'}, expiration='2019-01-30T20:04:37')

3. An expired cookie:

.. code-block:: bash

$ export FLASK_APP=app.py
$ flask cookie decode eyJhIjoiYXNkYXNkamtqYXNkIn0.XCkk1Q.tTPu2Zhvn9KxgkP35ERAgyd8MzA
ExpiredCookie(contents={'a': 'asdasdjkjasd'}, expiration='2019-01-30T20:04:37')

Documentation
=============

`Docs <https://flask-cookie-decode.readthedocs.io/en/latest/>`_

License
=======

`MIT <https://github.com/wgwz/flask-cookie-decode/blob/master/LICENSE>`_.


=======
History
=======

.. towncrier release notes start

Flask_Cookie_Decode 0.3.0 (2019-01-05)
======================================

Bugfixes
--------

- In all previous releases the CLI with the ``--timestamp`` CLI flag was actually
returning the timestamp when the cookie was signed. *Not* the timestamp when the
cookie expires, as it should have been doing.

In all previous releases there was no error handling for expired cookies. This
release now returns a ``ExpiredCookie`` when it is detected. (#1)


Improved Documentation
----------------------

- Updates the documentation to include some more details about the way the
Flask session works, and things you should be looking out for from a security
perspective. The documentation also reflects the latest in terms of the way
the CLI works. (#1)


0.1.0 (2018-12-29)
==================

* First release on PyPI.