path: root/docs/authentication.txt

=============================
User authentication in Django
=============================

Django comes with a user authentication system. It handles user accounts,
groups, permissions and cookie-based user sessions. This document explains how
things work.

The basics
==========

Django supports authentication out of the box. The ``django-admin.py init``
command, used to initialize a database with Django's core database tables,
creates the infrastructure for the auth system. You don't have to do anything
else to use authentication.

The auth system consists of:

    * Users
    * Permissions: Binary (yes/no) flags designating whether a user may perform
      a certain task.
    * Groups: A generic way of applying labels and permissions to more than one
      user.
    * Messages: A simple way to queue messages for given users.

Users
=====

Users are represented by a standard Django model, which lives in
`django/models/auth.py`_.

.. _django/models/auth.py: http://code.djangoproject.com/browser/django/trunk/django/models/auth.py

API reference
-------------

Fields
~~~~~~

``User`` objects have the following fields:

    * ``username`` -- Required. 30 characters or fewer. Alphanumeric characters
      only (letters, digits and underscores).
    * ``first_name`` -- Optional. 30 characters or fewer.
    * ``last_name`` -- Optional. 30 characters or fewer.
    * ``email`` -- Optional. E-mail address.
    * ``password_md5`` -- Required. An MD5 hash of the password. (Django
      doesn't store the raw password.) Raw passwords can be arbitrarily long
      and can contain any character.
    * ``is_staff`` -- Boolean. Designates whether this user can access the
      admin site.
    * ``is_active`` -- Boolean. Designates whether this user account is valid.
      Set this to ``False`` instead of deleting accounts.
    * ``is_superuser`` -- Boolean. Designates whether this user has permission
      to do anything (according to the permission system).
    * ``last_login`` -- A datetime of the user's last login. Is set to the
      current date/time by default.
    * ``date_joined`` -- A datetime designating when the account was created.
      Is set to the current date/time by default when the account is created.

Methods
~~~~~~~

``User`` objects have two many-to-many fields: ``groups`` and
``user_permissions``. Because of those relationships, ``User`` objects get
data-access methods like any other `Django model`_:

    * ``get_group_list(**kwargs)``
    * ``set_groups(id_list)``
    * ``get_permission_list(**kwargs)``
    * ``set_user_permissions(id_list)``

In addition to those automatic API methods, ``User`` objects have the following
methods:

    * ``is_anonymous()`` -- Always returns ``False``. This is a way of
      comparing ``User`` objects to anonymous users.

    * ``get_full_name()`` -- Returns the ``first_name`` plus the ``last_name``,
      with a space in between.

    * ``set_password(raw_password)`` -- Sets the user's password to the given
      raw string, taking care of the MD5 hashing. Doesn't save the ``User``
      object.

    * ``check_password(raw_password)`` -- Returns ``True`` if the given raw
      string is the correct password for the user.

    * ``get_group_permissions()`` -- Returns a list of permission strings that
      the user has, through his/her groups.

    * ``get_all_permissions()`` -- Returns a list of permission strings that
      the user has, both through group and user permissions.

    * ``has_perm(perm)`` -- Returns ``True`` if the user has the specified
      permission.

    * ``has_perms(perm_list)`` -- Returns ``True`` if the user has each of the
      specified permissions.

    * ``has_module_perms(package_name)`` -- Returns ``True`` if the user has
      any permissions in the given package (the Django app label).

    * ``get_and_delete_messages()`` -- Returns a list of ``Message`` objects in
      the user's queue and deletes the messages from the queue.

    * ``email_user(subject, message, from_email=None)`` -- Sends an e-mail to
      the user. If ``from_email`` is ``None``, Django uses the
      `DEFAULT_FROM_EMAIL`_ setting.

    * ``get_profile()`` -- Returns a site-specific profile for this user.
      Raises ``django.models.auth.SiteProfileNotAvailable`` if the current site
      doesn't allow profiles.

.. _Django model: http://www.djangoproject.com/documentation/model_api/
.. _DEFAULT_FROM_EMAIL: http://www.djangoproject.com/documentation/settings/#default-from-email

Module functions
~~~~~~~~~~~~~~~~

The ``django.models.auth.users`` module has the following helper functions:

    * ``create_user(username, email, password)`` -- Creates, saves and returns
      a ``User``. The ``username``, ``email`` and ``password`` are set as
      given, and the ``User`` gets ``is_active=True``.

    * ``make_random_password(length=10, allowed_chars='abcdefghjkmnpqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ23456789')``
      -- Returns a random password with the given length and given string of
      allowed characters. (Note that the default value of ``allowed_chars``
      doesn't contain ``"I"`` or letters that look like it, to avoid user
      confusion.

Basic usage
-----------

Creating users
~~~~~~~~~~~~~~

The most basic way to create users is to use the standard Django
`database API`_. Just create and save a ``User`` object::

    >>> from django.models.auth import users
    >>> import md5
    >>> p = md5.new('johnpassword').hexdigest()
    >>> u = users.User(username='john', first_name='John', last_name='lennon',
    ...     email='lennon@thebeatles.com', password_md5=p, is_staff=True,
    ...     is_active=True, is_superuser=False)
    >>> u.save()

Note that ``password_md5`` requires the raw MD5 hash. Because that's a pain,
there's a ``create_user`` helper function::

    >>> from django.models.auth import users
    >>> u = users.create_user('john', 'lennon@thebeatles.com', 'johnpassword')

.. _database API: http://www.djangoproject.com/documentation/db_api/

Changing passwords
~~~~~~~~~~~~~~~~~~

Change a password with ``set_password()``::

    >>> from django.models.auth import users
    >>> u = users.get_object(username__exact='john')
    >>> u.set_password('new password')
    >>> u.save()

Anonymous users
---------------

``django.parts.auth.anonymoususers.AnonymousUser`` is a class that implements
the ``django.models.auth.users.User`` interface, with these differences:

    * ``is_anonymous()`` returns ``True`` instead of ``False``.
    * ``has_perm()`` always returns ``False``.
    * ``set_password()``, ``check_password()``, ``set_groups()`` and
      ``set_permissions()`` raise ``NotImplementedError``.

In practice, you probably won't need to use ``AnonymousUser`` objects on your
own, but they're used by Web requests, as explained in the next section.

Authentication in Web requests
==============================

Until now, this document has dealt with the low-level APIs for manipulating
authentication-related objects. On a higher level, Django hooks this
authentication framework into its system of `request objects`_.

In any Django view, ``request.user`` will give you a ``User`` object
representing the currently logged-in user. If a user isn't currently logged in,
``request.user`` will be set to an instance of ``AnonymousUser`` (see the
previous section). You can tell them apart with ``is_anonymous()``, like so::

    if request.user.is_anonymous():
        # Do something for anonymous users.
    else:
        # Do something for logged-in users.

.. _request objects: http://www.djangoproject.com/documentation/request_response/#httprequest-objects

Limiting access to logged-in users
----------------------------------

The raw way
~~~~~~~~~~~

The simple, raw way to limit access to pages is to check
``request.user.is_anonymous()`` and either redirect to a login page::

    from django.utils.httpwrappers import HttpResponseRedirect

    def my_view(request):
        if request.user.is_anonymous():
            return HttpResponseRedirect('/login/?next=%s' % request.path)
        # ...

...or display an error message::

    def my_view(request):
        if request.user.is_anonymous():
            return render_to_response('myapp/login_error')
        # ...

The login_required decorator
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As a shortcut, you can use the convenient ``login_required`` decorator::

    from django.views.decorators.auth import login_required

    def my_view(request):
        # ...
    my_view = login_required(my_view)

Here's the same thing, using Python 2.4's decorator syntax::

    from django.views.decorators.auth import login_required

    @login_required
    def my_view(request):
        # ...

``login_required`` does the following:

    * If the user isn't logged in, redirect to ``/accounts/login/``, passing
      the current absolute URL in the query string as ``next``. For example:
      ``/accounts/login/?next=/polls/3/``.
    * If the user is logged in, execute the view normally. The view code is
      free to assume the user is logged in.

Limiting access to logged-in users that pass a test
---------------------------------------------------

To limit access based on certain permissions or another test, you'd do the same
thing as described in the previous section.

The simple way is to run your test on ``request.user`` in the view directly.
For example, this view checks to make sure the user is logged in and has the
permission ``polls.can_vote``::

    def my_view(request):
        if request.user.is_anonymous() or not request.user.has_perm('polls.can_vote'):
            return HttpResponse("You can't vote in this poll.")
        # ...

As a shortcut, you can use the convenient ``user_passes_test`` decorator::

    from django.views.decorators.auth import user_passes_test

    @user_passes_test(lambda u: u.has_perm('polls.can_vote'))
    def my_view(request):
        # ...

``user_passes_test`` takes a required argument: a callable that takes a
``User`` object and returns ``True`` if the user is allowed to view the page.
Note that ``user_passes_test`` does not automatically check that the ``User``
is not anonymous.



Permissions
===========

Groups
======

Messages
========