django/docs/topics/auth.txt

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

.. module:: django.contrib.auth
   :synopsis: Django's authentication framework.

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

Overview
========

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.

.. deprecated:: 1.2
   The Messages component of the auth system will be removed in Django 1.4.

Installation
============

Authentication support is bundled as a Django application in
``django.contrib.auth``. To install it, do the following:

    1. Put ``'django.contrib.auth'`` and ``'django.contrib.contenttypes'`` in
       your :setting:`INSTALLED_APPS` setting.
       (The :class:`~django.contrib.auth.models.Permission` model in
       :mod:`django.contrib.auth` depends on :mod:`django.contrib.contenttypes`.)
    2. Run the command ``manage.py syncdb``.

Note that the default :file:`settings.py` file created by
:djadmin:`django-admin.py startproject <startproject>` includes
``'django.contrib.auth'`` and ``'django.contrib.contenttypes'`` in
:setting:`INSTALLED_APPS` for convenience.  If your :setting:`INSTALLED_APPS`
already contains these apps, feel free to run :djadmin:`manage.py syncdb
<syncdb>` again; you can run that command as many times as you'd like, and each
time it'll only install what's needed.

The :djadmin:`syncdb` command creates the necessary database tables, creates
permission objects for all installed apps that need 'em, and prompts you to
create a superuser account the first time you run it.

Once you've taken those steps, that's it.

Users
=====

.. class:: models.User

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

Fields
~~~~~~

.. class:: models.User

    :class:`~django.contrib.auth.models.User` objects have the following
    fields:

    .. attribute:: models.User.username

        Required. 30 characters or fewer. Alphanumeric characters only
        (letters, digits and underscores).

        .. versionchanged:: 1.2
           Usernames may now contain ``@``, ``+``, ``.`` and ``-`` characters.

    .. attribute:: models.User.first_name

        Optional. 30 characters or fewer.

    .. attribute:: models.User.last_name

        Optional. 30 characters or fewer.

    .. attribute:: models.User.email

        Optional. E-mail address.

    .. attribute:: models.User.password

        Required. A hash of, and metadata about, the password. (Django doesn't
        store the raw password.) Raw passwords can be arbitrarily long and can
        contain any character. See the "Passwords" section below.

    .. attribute:: models.User.is_staff

        Boolean. Designates whether this user can access the admin site.

    .. attribute:: models.User.is_active

        Boolean. Designates whether this user account should be considered
        active. We recommend that you set this flag to ``False`` instead of
        deleting accounts; that way, if your applications have any foreign keys
        to users, the foreign keys won't break.

        This doesn't necessarily control whether or not the user can log in.
        Authentication backends aren't required to check for the ``is_active``
        flag, so if you want to reject a login based on ``is_active`` being
        ``False``, it's up to you to check that in your own login view.
        However, the :class:`~django.contrib.auth.forms.AuthenticationForm`
        used by the :func:`~django.contrib.auth.views.login` view *does*
        perform this check, as do the permission-checking methods such as
        :meth:`~models.User.has_perm` and the authentication in the Django
        admin. All of those functions/methods will return ``False`` for
        inactive users.

    .. attribute:: models.User.is_superuser

        Boolean. Designates that this user has all permissions without
        explicitly assigning them.

    .. attribute:: models.User.last_login

        A datetime of the user's last login. Is set to the current date/time by
        default.

    .. attribute:: models.User.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
~~~~~~~

.. class:: models.User

    :class:`~django.contrib.auth.models.User` objects have two many-to-many
    fields: models.User. ``groups`` and ``user_permissions``.
    :class:`~django.contrib.auth.models.User` objects can access their related
    objects in the same way as any other :doc:`Django model
    </topics/db/models>`:

    .. code-block:: python

        myuser.groups = [group_list]
        myuser.groups.add(group, group, ...)
        myuser.groups.remove(group, group, ...)
        myuser.groups.clear()
        myuser.user_permissions = [permission_list]
        myuser.user_permissions.add(permission, permission, ...)
        myuser.user_permissions.remove(permission, permission, ...)
        myuser.user_permissions.clear()

    In addition to those automatic API methods,
    :class:`~django.contrib.auth.models.User` objects have the following custom
    methods:

    .. method:: models.User.is_anonymous()

        Always returns ``False``. This is a way of differentiating
        :class:`~django.contrib.auth.models.User` and
        :class:`~django.contrib.auth.models.AnonymousUser` objects.
        Generally, you should prefer using
        :meth:`~django.contrib.auth.models.User.is_authenticated()` to this
        method.

    .. method:: models.User.is_authenticated()

        Always returns ``True``. This is a way to tell if the user has been
        authenticated. This does not imply any permissions, and doesn't check
        if the user is active - it only indicates that the user has provided a
        valid username and password.

    .. method:: models.User.get_full_name()

        Returns the :attr:`~django.contrib.auth.models.User.first_name` plus
        the :attr:`~django.contrib.auth.models.User.last_name`, with a space in
        between.

    .. method:: models.User.set_password(raw_password)

        Sets the user's password to the given raw string, taking care of the
        password hashing. Doesn't save the
        :class:`~django.contrib.auth.models.User` object.

    .. method:: models.User.check_password(raw_password)

        Returns ``True`` if the given raw string is the correct password for
        the user. (This takes care of the password hashing in making the
        comparison.)

    .. method:: models.User.set_unusable_password()

        Marks the user as having no password set.  This isn't the same as
        having a blank string for a password.
        :meth:`~django.contrib.auth.models.User.check_password()` for this user
        will never return ``True``. Doesn't save the
        :class:`~django.contrib.auth.models.User` object.

        You may need this if authentication for your application takes place
        against an existing external source such as an LDAP directory.

    .. method:: models.User.has_usable_password()

        Returns ``False`` if
        :meth:`~django.contrib.auth.models.User.set_unusable_password()` has
        been called for this user.

    .. method:: models.User.get_group_permissions(obj=None)

        Returns a set of permission strings that the user has, through his/her
        groups.

        .. versionadded:: 1.2

        If ``obj`` is passed in, only returns the group permissions for
        this specific object.

    .. method:: models.User.get_all_permissions(obj=None)

        Returns a set of permission strings that the user has, both through
        group and user permissions.

        .. versionadded:: 1.2

        If ``obj`` is passed in, only returns the permissions for this
        specific object.

    .. method:: models.User.has_perm(perm, obj=None)

        Returns ``True`` if the user has the specified permission, where perm is
        in the format ``"<app label>.<permission codename>"``. (see
        `permissions`_ section below). If the user is inactive, this method will
        always return ``False``.

        .. versionadded:: 1.2

        If ``obj`` is passed in, this method won't check for a permission for
        the model, but for this specific object.

    .. method:: models.User.has_perms(perm_list, obj=None)

        Returns ``True`` if the user has each of the specified permissions,
        where each perm is in the format
        ``"<app label>.<permission codename>"``. If the user is inactive,
        this method will always return ``False``.

        .. versionadded:: 1.2

        If ``obj`` is passed in, this method won't check for permissions for
        the model, but for the specific object.

    .. method:: models.User.has_module_perms(package_name)

        Returns ``True`` if the user has any permissions in the given package
        (the Django app label). If the user is inactive, this method will
        always return ``False``.

    .. method:: models.User.get_and_delete_messages()

        Returns a list of :class:`~django.contrib.auth.models.Message` objects
        in the user's queue and deletes the messages from the queue.

    .. method:: models.User.email_user(subject, message, from_email=None)

        Sends an e-mail to the user. If
        :attr:`~django.contrib.auth.models.User.from_email` is ``None``, Django
        uses the :setting:`DEFAULT_FROM_EMAIL`.

    .. method:: models.User.get_profile()

        Returns a site-specific profile for this user. Raises
        :exc:`django.contrib.auth.models.SiteProfileNotAvailable` if the
        current site doesn't allow profiles. For information on how to define a
        site-specific user profile, see the section on `storing additional user
        information`_ below.

.. _storing additional user information: #storing-additional-information-about-users

Manager functions
~~~~~~~~~~~~~~~~~

.. class:: models.UserManager

    The :class:`~django.contrib.auth.models.User` model has a custom manager
    that has the following helper functions:

    .. method:: models.UserManager.create_user(username, email, password=None)

        Creates, saves and returns a :class:`~django.contrib.auth.models.User`.

        The :attr:`~django.contrib.auth.models.User.username` and
        :attr:`~django.contrib.auth.models.User.password` are set as given. The
        domain portion of :attr:`~django.contrib.auth.models.User.email` is
        automatically convered to lowercase, and the returned
        :class:`~django.contrib.auth.models.User` object will have
        :attr:`~models.User.is_active` set to ``True``.

        If no password is provided,
        :meth:`~django.contrib.auth.models.User.set_unusable_password()` will
        be called.

        See `Creating users`_ for example usage.

    .. method:: models.UserManager.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 letters that can cause user confusion, including:

            * ``i``, ``l``, ``I``, and ``1`` (lowercase letter i, lowercase
              letter L, uppercase letter i, and the number one)
            * ``o``, ``O``, and ``0`` (uppercase letter o, lowercase letter o,
              and zero)

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

.. _topics-auth-creating-users:

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

The most basic way to create users is to use the
:meth:`~django.contrib.auth.models.UserManager.create_user` helper function
that comes with Django::

    >>> from django.contrib.auth.models import User
    >>> user = User.objects.create_user('john', 'lennon@thebeatles.com', 'johnpassword')

    # At this point, user is a User object that has already been saved
    # to the database. You can continue to change its attributes
    # if you want to change other fields.
    >>> user.is_staff = True
    >>> user.save()

You can also create users using the Django admin site. Assuming you've enabled
the admin site and hooked it to the URL ``/admin/``, the "Add user" page is at
``/admin/auth/user/add/``. You should also see a link to "Users" in the "Auth"
section of the main admin index page. The "Add user" admin page is different
than standard admin pages in that it requires you to choose a username and
password before allowing you to edit the rest of the user's fields.

Also note: if you want your own user account to be able to create users using
the Django admin site, you'll need to give yourself permission to add users
*and* change users (i.e., the "Add user" and "Change user" permissions). If
your account has permission to add users but not to change them, you won't be
able to add users. Why? Because if you have permission to add users, you have
the power to create superusers, which can then, in turn, change other users. So
Django requires add *and* change permissions as a slight security measure.

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

.. versionadded:: 1.2
   The ``manage.py changepassword`` command was added.

:djadmin:`manage.py changepassword *username* <changepassword>` offers a method
of changing a User's password from the command line. It prompts you to
change the password of a given user which you must enter twice. If
they both match, the new password will be changed immediately. If you
do not supply a user, the command will attempt to change the password
whose username matches the current user.

You can also change a password programmatically, using
:meth:`~django.contrib.auth.models.User.set_password()`:

.. code-block:: python

    >>> from django.contrib.auth.models import User
    >>> u = User.objects.get(username__exact='john')
    >>> u.set_password('new password')
    >>> u.save()

Don't set the :attr:`~django.contrib.auth.models.User.password` attribute
directly unless you know what you're doing. This is explained in the next
section.

Passwords
---------

The :attr:`~django.contrib.auth.models.User.password` attribute of a
:class:`~django.contrib.auth.models.User` object is a string in this format::

    hashtype$salt$hash

That's hashtype, salt and hash, separated by the dollar-sign character.

Hashtype is either ``sha1`` (default), ``md5`` or ``crypt`` -- the algorithm
used to perform a one-way hash of the password. Salt is a random string used
to salt the raw password to create the hash. Note that the ``crypt`` method is
only supported on platforms that have the standard Python ``crypt`` module
available.

For example::

    sha1$a1976$a36cc8cbf81742a8fb52e221aaeab48ed7f58ab4

The :meth:`~django.contrib.auth.models.User.set_password` and
:meth:`~django.contrib.auth.models.User.check_password` functions handle the
setting and checking of these values behind the scenes.

Previous Django versions, such as 0.90, used simple MD5 hashes without password
salts. For backwards compatibility, those are still supported; they'll be
converted automatically to the new style the first time
:meth:`~django.contrib.auth.models.User.check_password()` works correctly for
a given user.

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

.. class:: models.AnonymousUser

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

    * :attr:`~django.contrib.auth.models.User.id` is always ``None``.
    * :attr:`~django.contrib.auth.models.User.is_staff` and
      :attr:`~django.contrib.auth.models.User.is_superuser` are always
      ``False``.
    * :attr:`~django.contrib.auth.models.User.is_active` is always ``False``.
    * :attr:`~django.contrib.auth.models.User.groups` and
      :attr:`~django.contrib.auth.models.User.user_permissions` are always
      empty.
    * :meth:`~django.contrib.auth.models.User.is_anonymous()` returns ``True``
      instead of ``False``.
    * :meth:`~django.contrib.auth.models.User.is_authenticated()` returns
      ``False`` instead of ``True``.
    * :meth:`~django.contrib.auth.models.User.set_password()`,
      :meth:`~django.contrib.auth.models.User.check_password()`,
      :meth:`~django.contrib.auth.models.User.save()`,
      :meth:`~django.contrib.auth.models.User.delete()`,
      :meth:`~django.contrib.auth.models.User.set_groups()` and
      :meth:`~django.contrib.auth.models.User.set_permissions()` raise
      :exc:`NotImplementedError`.

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

.. _topics-auth-creating-superusers:

Creating superusers
-------------------

:djadmin:`manage.py syncdb <syncdb>` prompts you to create a superuser the
first time you run it after adding ``'django.contrib.auth'`` to your
:setting:`INSTALLED_APPS`. If you need to create a superuser at a later date,
you can use a command line utility::

    manage.py createsuperuser --username=joe --email=joe@example.com

You will be prompted for a password. After you enter one, the user will be
created immediately. If you leave off the :djadminopt:`--username` or the
:djadminopt:`--email` options, it will prompt you for those values.

If you're using an older release of Django, the old way of creating a superuser
on the command line still works::

    python /path/to/django/contrib/auth/create_superuser.py

...where :file:`/path/to` is the path to the Django codebase on your
filesystem. The ``manage.py`` command is preferred because it figures out the
correct path and environment for you.

.. _auth-profiles:

Storing additional information about users
------------------------------------------

If you'd like to store additional information related to your users, Django
provides a method to specify a site-specific related model -- termed a "user
profile" -- for this purpose.

To make use of this feature, define a model with fields for the
additional information you'd like to store, or additional methods
you'd like to have available, and also add a
:class:`~django.db.models.Field.OneToOneField` from your model to the
:class:`~django.contrib.auth.models.User` model. This will ensure only
one instance of your model can be created for each
:class:`~django.contrib.auth.models.User`.

To indicate that this model is the user profile model for a given site, fill in
the setting :setting:`AUTH_PROFILE_MODULE` with a string consisting of the
following items, separated by a dot:

1. The name of the application (case sensitive) in which the user
   profile model is defined (in other words, the
   name which was passed to :djadmin:`manage.py startapp <startapp>` to create
   the application).

2. The name of the model (not case sensitive) class.

For example, if the profile model was a class named ``UserProfile`` and was
defined inside an application named ``accounts``, the appropriate setting would
be::

    AUTH_PROFILE_MODULE = 'accounts.UserProfile'

When a user profile model has been defined and specified in this manner, each
:class:`~django.contrib.auth.models.User` object will have a method --
:class:`~django.contrib.auth.models.User.get_profile()` -- which returns the
instance of the user profile model associated with that
:class:`~django.contrib.auth.models.User`.

The method :class:`~django.contrib.auth.models.User.get_profile()`
does not create the profile, if it does not exist. You need to
register a handler for the signal
:attr:`django.db.models.signals.post_save` on the User model, and, in
the handler, if created=True, create the associated user profile.

For more information, see `Chapter 12 of the Django book`_.

.. _Chapter 12 of the Django book: http://www.djangobook.com/en/1.0/chapter12/#cn222

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 can hook this
authentication framework into its system of
:class:`request objects <django.http.HttpRequest>`.

First, install the
:class:`~django.contrib.sessions.middleware.SessionMiddleware` and
:class:`~django.contrib.auth.middleware.AuthenticationMiddleware`
middlewares by adding them to your :setting:`MIDDLEWARE_CLASSES` setting. See
the :doc:`session documentation </topics/http/sessions>` for more information.

Once you have those middlewares installed, you'll be able to access
:attr:`request.user <django.http.HttpRequest.user>` in views.
:attr:`request.user <django.http.HttpRequest.user>` will give you a
:class:`~django.contrib.auth.models.User` object representing the currently
logged-in user. If a user isn't currently logged in,
:attr:`request.user <django.http.HttpRequest.user>` will be set to an instance
of :class:`~django.contrib.auth.models.AnonymousUser` (see the previous
section). You can tell them apart with
:meth:`~django.contrib.auth.models.User.is_authenticated()`, like so::

    if request.user.is_authenticated():
        # Do something for authenticated users.
    else:
        # Do something for anonymous users.

.. _how-to-log-a-user-in:

How to log a user in
--------------------

Django provides two functions in :mod:`django.contrib.auth`:
:func:`~django.contrib.auth.authenticate()` and
:func:`~django.contrib.auth.login()`.

.. function:: authenticate()

    To authenticate a given username and password, use
    :func:`~django.contrib.auth.authenticate()`. It takes two keyword
    arguments, ``username`` and ``password``, and it returns a
    :class:`~django.contrib.auth.models.User` object if the password is valid
    for the given username. If the password is invalid,
    :func:`~django.contrib.auth.authenticate()` returns ``None``. Example::

        from django.contrib.auth import authenticate
        user = authenticate(username='john', password='secret')
        if user is not None:
            if user.is_active:
                print "You provided a correct username and password!"
            else:
                print "Your account has been disabled!"
        else:
            print "Your username and password were incorrect."

.. function:: login()

    To log a user in, in a view, use :func:`~django.contrib.auth.login()`. It
    takes an :class:`~django.http.HttpRequest` object and a
    :class:`~django.contrib.auth.models.User` object.
    :func:`~django.contrib.auth.login()` saves the user's ID in the session,
    using Django's session framework, so, as mentioned above, you'll need to
    make sure to have the session middleware installed.

    This example shows how you might use both
    :func:`~django.contrib.auth.authenticate()` and
    :func:`~django.contrib.auth.login()`::

        from django.contrib.auth import authenticate, login

        def my_view(request):
            username = request.POST['username']
            password = request.POST['password']
            user = authenticate(username=username, password=password)
            if user is not None:
                if user.is_active:
                    login(request, user)
                    # Redirect to a success page.
                else:
                    # Return a 'disabled account' error message
            else:
                # Return an 'invalid login' error message.

.. admonition:: Calling ``authenticate()`` first

    When you're manually logging a user in, you *must* call
    :func:`~django.contrib.auth.authenticate()` before you call
    :func:`~django.contrib.auth.login()`.
    :func:`~django.contrib.auth.authenticate()`
    sets an attribute on the :class:`~django.contrib.auth.models.User` noting
    which authentication backend successfully authenticated that user (see the
    `backends documentation`_ for details), and this information is needed
    later during the login process.

.. _backends documentation: #other-authentication-sources

Manually checking a user's password
-----------------------------------

.. currentmodule:: django.contrib.auth.models

.. function:: check_password()

    If you'd like to manually authenticate a user by comparing a plain-text
    password to the hashed password in the database, use the convenience
    function :func:`django.contrib.auth.models.check_password`. It takes two
    arguments: the plain-text password to check, and the full value of a user's
    ``password`` field in the database to check against, and returns ``True``
    if they match, ``False`` otherwise.

How to log a user out
---------------------

.. currentmodule:: django.contrib.auth

.. function:: logout()

    To log out a user who has been logged in via
    :func:`django.contrib.auth.login()`, use
    :func:`django.contrib.auth.logout()` within your view. It takes an
    :class:`~django.http.HttpRequest` object and has no return value.
    Example::

        from django.contrib.auth import logout

        def logout_view(request):
            logout(request)
            # Redirect to a success page.

    Note that :func:`~django.contrib.auth.logout()` doesn't throw any errors if
    the user wasn't logged in.

    When you call :func:`~django.contrib.auth.logout()`, the session data for
    the current request is completely cleaned out. All existing data is
    removed. This is to prevent another person from using the same Web browser
    to log in and have access to the previous user's session data. If you want
    to put anything into the session that will be available to the user
    immediately after logging out, do that *after* calling
    :func:`django.contrib.auth.logout()`.

.. _topics-auth-signals:

Login and logout signals
------------------------

.. versionadded:: 1.3

The auth framework uses two :doc:`signals </topics/signals>` that can be used
for notification when a user logs in or out.

.. data:: django.contrib.auth.signals.user_logged_in

Sent when a user logs in successfully.

Arguments sent with this signal:

    ``sender``
        As above: the class of the user that just logged in.

    ``request``
        The current :class:`~django.http.HttpRequest` instance.

    ``user``
        The user instance that just logged in.

.. data:: django.contrib.auth.signals.user_logged_out

Sent when the logout method is called.

    ``sender``
        As above: the class of the user that just logged out or ``None``
        if the user was not authenticated.

    ``request``
        The current :class:`~django.http.HttpRequest` instance.

    ``user``
        The user instance that just logged out or ``None`` if the
        user was not authenticated.

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

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

The simple, raw way to limit access to pages is to check
:meth:`request.user.is_authenticated()
<django.contrib.auth.models.User.is_authenticated()>` and either redirect to a
login page::

    from django.http import HttpResponseRedirect

    def my_view(request):
        if not request.user.is_authenticated():
            return HttpResponseRedirect('/login/?next=%s' % request.path)
        # ...

...or display an error message::

    def my_view(request):
        if not request.user.is_authenticated():
            return render_to_response('myapp/login_error.html')
        # ...

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

.. function:: decorators.login_required([redirect_field_name=REDIRECT_FIELD_NAME, login_url=None])

    As a shortcut, you can use the convenient
    :func:`~django.contrib.auth.decorators.login_required` decorator::

        from django.contrib.auth.decorators import login_required

        @login_required
        def my_view(request):
            ...

    :func:`~django.contrib.auth.decorators.login_required` does the following:

    * If the user isn't logged in, redirect to
      :setting:`settings.LOGIN_URL <LOGIN_URL>`, passing the current absolute
      path in the query string. 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.

    By default, the path that the user should be redirected to upon
    successful authentication is stored in a query string parameter called
    ``"next"``. If you would prefer to use a different name for this parameter,
    :func:`~django.contrib.auth.decorators.login_required` takes an
    optional ``redirect_field_name`` parameter::

        from django.contrib.auth.decorators import login_required

        @login_required(redirect_field_name='my_redirect_field')
        def my_view(request):
            ...

    Note that if you provide a value to ``redirect_field_name``, you will most
    likely need to customize your login template as well, since the template
    context variable which stores the redirect path will use the value of
    ``redirect_field_name`` as it's key rather than ``"next"`` (the default).

    .. versionadded:: 1.3

    :func:`~django.contrib.auth.decorators.login_required` also takes an
    optional ``login_url`` parameter. Example::

        from django.contrib.auth.decorators import login_required

        @login_required(login_url='/accounts/login/')
        def my_view(request):
            ...

    Note that if you don't specify the ``login_url`` parameter, you'll need to map
    the appropriate Django view to :setting:`settings.LOGIN_URL <LOGIN_URL>`. For
    example, using the defaults, add the following line to your URLconf::

        (r'^accounts/login/$', 'django.contrib.auth.views.login'),

.. function:: views.login(request, [template_name, redirect_field_name, authentication_form])

    Here's what ``django.contrib.auth.views.login`` does:

        * If called via ``GET``, it displays a login form that POSTs to the
          same URL. More on this in a bit.

        * If called via ``POST``, it tries to log the user in. If login is
          successful, the view redirects to the URL specified in ``next``. If
          ``next`` isn't provided, it redirects to
          :setting:`settings.LOGIN_REDIRECT_URL <LOGIN_REDIRECT_URL>` (which
          defaults to ``/accounts/profile/``). If login isn't successful, it
          redisplays the login form.

    It's your responsibility to provide the login form in a template called
    ``registration/login.html`` by default. This template gets passed four
    template context variables:

        * ``form``: A :class:`~django.forms.Form` object representing the login
          form. See the :doc:`forms documentation </topics/forms/index>` for
          more on ``Form`` objects.

        * ``next``: The URL to redirect to after successful login. This may
          contain a query string, too.

        * ``site``: The current :class:`~django.contrib.sites.models.Site`,
          according to the :setting:`SITE_ID` setting. If you don't have the
          site framework installed, this will be set to an instance of
          :class:`~django.contrib.sites.models.RequestSite`, which derives the
          site name and domain from the current
          :class:`~django.http.HttpRequest`.

        * ``site_name``: An alias for ``site.name``. If you don't have the site
          framework installed, this will be set to the value of
          :attr:`request.META['SERVER_NAME'] <django.http.HttpRequest.META>`.
          For more on sites, see :doc:`/ref/contrib/sites`.

    If you'd prefer not to call the template :file:`registration/login.html`,
    you can pass the ``template_name`` parameter via the extra arguments to
    the view in your URLconf. For example, this URLconf line would use
    :file:`myapp/login.html` instead::

        (r'^accounts/login/$', 'django.contrib.auth.views.login', {'template_name': 'myapp/login.html'}),

    You can also specify the name of the ``GET`` field which contains the URL
    to redirect to after login by passing ``redirect_field_name`` to the view.
    By default, the field is called ``next``.

    Here's a sample :file:`registration/login.html` template you can use as a
    starting point. It assumes you have a :file:`base.html` template that
    defines a ``content`` block:

    .. code-block:: html+django

        {% extends "base.html" %}
        {% load url from future %}

        {% block content %}

        {% if form.errors %}
        <p>Your username and password didn't match. Please try again.</p>
        {% endif %}

        <form method="post" action="{% url 'django.contrib.auth.views.login' %}">
        {% csrf_token %}
        <table>
        <tr>
            <td>{{ form.username.label_tag }}</td>
            <td>{{ form.username }}</td>
        </tr>
        <tr>
            <td>{{ form.password.label_tag }}</td>
            <td>{{ form.password }}</td>
        </tr>
        </table>

        <input type="submit" value="login" />
        <input type="hidden" name="next" value="{{ next }}" />
        </form>

        {% endblock %}

    .. versionadded:: 1.2

    If you are using alternate authentication (see
    :ref:`authentication-backends`) you can pass a custom authentication form
    to the login view via the ``authentication_form`` parameter. This form must
    accept a ``request`` keyword argument in its ``__init__`` method, and
    provide a ``get_user`` method which returns the authenticated user object
    (this method is only ever called after successful form validation).

    .. _forms documentation: ../forms/
    .. _site framework docs: ../sites/

Other built-in views
--------------------

.. module:: django.contrib.auth.views

In addition to the :func:`~views.login` view, the authentication system
includes a few other useful built-in views located in
:mod:`django.contrib.auth.views`:

.. function:: logout(request, [next_page, template_name, redirect_field_name])

    Logs a user out.

    **Optional arguments:**

        * ``next_page``: The URL to redirect to after logout.

        * ``template_name``: The full name of a template to display after
          logging the user out. This will default to
          :file:`registration/logged_out.html` if no argument is supplied.

        * ``redirect_field_name``: The name of a ``GET`` field containing the
          URL to redirect to after log out. Overrides ``next_page`` if the given
          ``GET`` parameter is passed.

    **Template context:**

        * ``title``: The string "Logged out", localized.

.. function:: logout_then_login(request[, login_url])

    Logs a user out, then redirects to the login page.

    **Optional arguments:**

        * ``login_url``: The URL of the login page to redirect to. This will
          default to :setting:`settings.LOGIN_URL <LOGIN_URL>` if not supplied.

.. function:: password_change(request[, template_name, post_change_redirect, password_change_form])

    Allows a user to change their password.

    **Optional arguments:**

        * ``template_name``: The full name of a template to use for
          displaying the password change form. This will default to
          :file:`registration/password_change_form.html` if not supplied.

        * ``post_change_redirect``: The URL to redirect to after a successful
          password change.

        * .. versionadded:: 1.2

          ``password_change_form``: A custom "change password" form which must
          accept a ``user`` keyword argument. The form is responsible for
          actually changing the user's password.


    **Template context:**

        * ``form``: The password change form.

.. function:: password_change_done(request[, template_name])

    The page shown after a user has changed their password.

    **Optional arguments:**

        * ``template_name``: The full name of a template to use. This will
          default to :file:`registration/password_change_done.html` if not
          supplied.

.. function:: password_reset(request[, is_admin_site, template_name, email_template_name, password_reset_form, token_generator, post_reset_redirect, from_email])

    Allows a user to reset their password by generating a one-time use link
    that can be used to reset the password, and sending that link to the
    user's registered e-mail address.

    .. versionchanged:: 1.3
        The ``from_email`` argument was added.

    **Optional arguments:**

        * ``template_name``: The full name of a template to use for
          displaying the password reset form. This will default to
          :file:`registration/password_reset_form.html` if not supplied.

        * ``email_template_name``: The full name of a template to use for
          generating the e-mail with the new password. This will default to
          :file:`registration/password_reset_email.html` if not supplied.

        * ``password_reset_form``: Form that will be used to set the password.
          Defaults to :class:`~django.contrib.auth.forms.PasswordResetForm`.

        * ``token_generator``: Instance of the class to check the password. This
          will default to ``default_token_generator``, it's an instance of
          ``django.contrib.auth.tokens.PasswordResetTokenGenerator``.

        * ``post_reset_redirect``: The URL to redirect to after a successful
          password change.

        * ``from_email``: A valid e-mail address. By default Django uses
          the :setting:`DEFAULT_FROM_EMAIL`.

    **Template context:**

        * ``form``: The form for resetting the user's password.

.. function:: password_reset_done(request[, template_name])

    The page shown after a user has reset their password.

    **Optional arguments:**

        * ``template_name``: The full name of a template to use. This will
          default to :file:`registration/password_reset_done.html` if not
          supplied.

.. function:: redirect_to_login(next[, login_url, redirect_field_name])

    Redirects to the login page, and then back to another URL after a
    successful login.

    **Required arguments:**

        * ``next``: The URL to redirect to after a successful login.

    **Optional arguments:**

        * ``login_url``: The URL of the login page to redirect to. This will
          default to :setting:`settings.LOGIN_URL <LOGIN_URL>` if not supplied.

        * ``redirect_field_name``: The name of a ``GET`` field containing the
          URL to redirect to after log out. Overrides ``next`` if the given
          ``GET`` parameter is passed.


.. function:: password_reset_confirm(request[, uidb36, token, template_name, token_generator, set_password_form, post_reset_redirect])

    Presents a form for entering a new password.

    **Optional arguments:**

        * ``uidb36``: The user's id encoded in base 36. This will default to
          ``None``.
        * ``token``: Token to check that the password is valid. This will default to ``None``.
        * ``template_name``: The full name of a template to display the confirm
          password view. Default value is :file:`registration/password_reset_confirm.html`.
        * ``token_generator``: Instance of the class to check the password. This
          will default to ``default_token_generator``, it's an instance of
          ``django.contrib.auth.tokens.PasswordResetTokenGenerator``.
        * ``set_password_form``: Form that will be used to set the password.
          This will default to ``SetPasswordForm``.
        * ``post_reset_redirect``: URL to redirect after the password reset
          done. This will default to ``None``.

.. function:: password_reset_complete(request[,template_name])

   Presents a view which informs the user that the password has been
   successfully changed.

   **Optional arguments:**

       * ``template_name``: The full name of a template to display the view.
         This will default to :file:`registration/password_reset_complete.html`.

Built-in forms
--------------

.. module:: django.contrib.auth.forms

If you don't want to use the built-in views, but want the convenience of not
having to write forms for this functionality, the authentication system
provides several built-in forms located in :mod:`django.contrib.auth.forms`:

.. class:: AdminPasswordChangeForm

    A form used in the admin interface to change a user's password.

.. class:: AuthenticationForm

    A form for logging a user in.

.. class:: PasswordChangeForm

    A form for allowing a user to change their password.

.. class:: PasswordResetForm

    A form for generating and e-mailing a one-time use link to reset a
    user's password.

.. class:: SetPasswordForm

    A form that lets a user change his/her password without entering the old
    password.

.. class:: UserChangeForm

    A form used in the admin interface to change a user's information and
    permissions.

.. class:: UserCreationForm

    A form for creating a new user.

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

.. currentmodule:: django.contrib.auth.decorators

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

The simple way is to run your test on :attr:`request.user
<django.http.HttpRequest.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 not request.user.has_perm('polls.can_vote'):
            return HttpResponse("You can't vote in this poll.")
        # ...

.. function:: user_passes_test()

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

        from django.contrib.auth.decorators import user_passes_test

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

    We're using this particular test as a relatively simple example. However,
    if you just want to test whether a permission is available to a user, you
    can use the :func:`~django.contrib.auth.decorators.permission_required()`
    decorator, described later in this document.

    :func:`~django.contrib.auth.decorators.user_passes_test` takes a required
    argument: a callable that takes a
    :class:`~django.contrib.auth.models.User` object and returns ``True`` if
    the user is allowed to view the page. Note that
    :func:`~django.contrib.auth.decorators.user_passes_test` does not
    automatically check that the :class:`~django.contrib.auth.models.User` is
    not anonymous.

    :func:`~django.contrib.auth.decorators.user_passes_test()` takes an
    optional ``login_url`` argument, which lets you specify the URL for your
    login page (:setting:`settings.LOGIN_URL <LOGIN_URL>` by default).

    For example::

        from django.contrib.auth.decorators import user_passes_test

        @user_passes_test(lambda u: u.has_perm('polls.can_vote'), login_url='/login/')
        def my_view(request):
            ...

The permission_required decorator
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. function:: permission_required()

    It's a relatively common task to check whether a user has a particular
    permission. For that reason, Django provides a shortcut for that case: the
    :func:`~django.contrib.auth.decorators.permission_required()` decorator.
    Using this decorator, the earlier example can be written as::

        from django.contrib.auth.decorators import permission_required

        @permission_required('polls.can_vote')
        def my_view(request):
            ...

    As for the :meth:`User.has_perm` method, permission names take the form
    ``"<app label>.<permission codename>"`` (i.e. ``polls.can_vote`` for a
    permission on a model in the ``polls`` application).

    Note that :func:`~django.contrib.auth.decorators.permission_required()`
    also takes an optional ``login_url`` parameter. Example::

        from django.contrib.auth.decorators import permission_required

        @permission_required('polls.can_vote', login_url='/loginpage/')
        def my_view(request):
            ...

    As in the :func:`~decorators.login_required` decorator, ``login_url``
    defaults to :setting:`settings.LOGIN_URL <LOGIN_URL>`.

.. currentmodule:: django.contrib.auth

Limiting access to generic views
--------------------------------

To limit access to a :doc:`generic view </ref/generic-views>`, write a thin
wrapper around the view, and point your URLconf to your wrapper instead of the
generic view itself. For example::

    from django.views.generic.date_based import object_detail

    @login_required
    def limited_object_detail(*args, **kwargs):
        return object_detail(*args, **kwargs)

.. _permissions:

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

Django comes with a simple permissions system. It provides a way to assign
permissions to specific users and groups of users.

It's used by the Django admin site, but you're welcome to use it in your own
code.

The Django admin site uses permissions as follows:

    * Access to view the "add" form and add an object is limited to users with
      the "add" permission for that type of object.
    * Access to view the change list, view the "change" form and change an
      object is limited to users with the "change" permission for that type of
      object.
    * Access to delete an object is limited to users with the "delete"
      permission for that type of object.

Permissions are set globally per type of object, not per specific object
instance. For example, it's possible to say "Mary may change news stories," but
it's not currently possible to say "Mary may change news stories, but only the
ones she created herself" or "Mary may only change news stories that have a
certain status, publication date or ID." The latter functionality is something
Django developers are currently discussing.

Default permissions
-------------------

When ``django.contrib.auth`` is listed in your :setting:`INSTALLED_APPS`
setting, it will ensure that three default permissions -- add, change and
delete -- are created for each Django model defined in one of your installed
applications.

These permissions will be created when you run :djadmin:`manage.py syncdb
<syncdb>`; the first time you run ``syncdb`` after adding
``django.contrib.auth`` to :setting:`INSTALLED_APPS`, the default permissions
will be created for all previously-installed models, as well as for any new
models being installed at that time. Afterward, it will create default
permissions for new models each time you run :djadmin:`manage.py syncdb
<syncdb>`.

Assuming you have an application with an
:attr:`~django.db.models.Options.app_label` ``foo`` and a model named ``Bar``,
to test for basic permissions you should use:

    * add: ``user.has_perm('foo.add_bar')``
    * change: ``user.has_perm('foo.change_bar')``
    * delete: ``user.has_perm('foo.delete_bar')``

.. _custom-permissions:

Custom permissions
------------------

To create custom permissions for a given model object, use the ``permissions``
:ref:`model Meta attribute <meta-options>`.

This example Task model creates three custom permissions, i.e., actions users
can or cannot do with Task instances, specific to your appication::

    class Task(models.Model):
        ...
        class Meta:
            permissions = (
                ("can_view", "Can see available tasks"),
                ("can_change_status", "Can change the status of tasks"),
                ("can_close", "Can remove a task by setting its status as closed"),
            )

The only thing this does is create those extra permissions when you run
:djadmin:`manage.py syncdb <syncdb>`. Your code is in charge of checking the
value of these permissions when an user is trying to access the functionality
provided by the application (viewing tasks, changing the status of tasks,
closing tasks.)

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

.. currentmodule:: django.contrib.auth.models

.. class:: Permission

    Just like users, permissions are implemented in a Django model that lives
    in `django/contrib/auth/models.py`_.

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

Fields
~~~~~~

:class:`~django.contrib.auth.models.Permission` objects have the following
fields:

.. attribute:: Permission.name

    Required. 50 characters or fewer. Example: ``'Can vote'``.

.. attribute:: Permission.content_type

    Required. A reference to the ``django_content_type`` database table, which
    contains a record for each installed Django model.

.. attribute:: Permission.codename

    Required. 100 characters or fewer. Example: ``'can_vote'``.

Methods
~~~~~~~

:class:`~django.contrib.auth.models.Permission` objects have the standard
data-access methods like any other :doc:`Django model </ref/models/instances>`.

.. currentmodule:: django.contrib.auth

Authentication data in templates
================================

The currently logged-in user and his/her permissions are made available in the
:doc:`template context </ref/templates/api>` when you use
:class:`~django.template.context.RequestContext`.

.. admonition:: Technicality

   Technically, these variables are only made available in the template context
   if you use :class:`~django.template.context.RequestContext` *and* your
   :setting:`TEMPLATE_CONTEXT_PROCESSORS` setting contains
   ``"django.contrib.auth.context_processors.auth"``, which is default. For
   more, see the :ref:`RequestContext docs <subclassing-context-requestcontext>`.

Users
-----

When rendering a template :class:`~django.template.context.RequestContext`, the
currently logged-in user, either a  :class:`~django.contrib.auth.models.User`
instance or an :class:`~django.contrib.auth.models.AnonymousUser` instance, is
stored in the template variable ``{{ user }}``:

.. code-block:: html+django

    {% if user.is_authenticated %}
        <p>Welcome, {{ user.username }}. Thanks for logging in.</p>
    {% else %}
        <p>Welcome, new user. Please log in.</p>
    {% endif %}

This template context variable is not available if a ``RequestContext`` is not
being used.

Permissions
-----------

The currently logged-in user's permissions are stored in the template variable
``{{ perms }}``. This is an instance of
:class:`django.contrib.auth.context_processors.PermWrapper`, which is a
template-friendly proxy of permissions.

.. versionchanged:: 1.3
    Prior to version 1.3, ``PermWrapper`` was located in
    ``django.contrib.auth.context_processors``.

In the ``{{ perms }}`` object, single-attribute lookup is a proxy to
:meth:`User.has_module_perms <django.contrib.auth.models.User.has_module_perms>`.
This example would display ``True`` if the logged-in user had any permissions
in the ``foo`` app::

    {{ perms.foo }}

Two-level-attribute lookup is a proxy to
:meth:`User.has_perm <django.contrib.auth.models.User.has_perm>`. This example
would display ``True`` if the logged-in user had the permission
``foo.can_vote``::

    {{ perms.foo.can_vote }}

Thus, you can check permissions in template ``{% if %}`` statements:

.. code-block:: html+django

    {% if perms.foo %}
        <p>You have permission to do something in the foo app.</p>
        {% if perms.foo.can_vote %}
            <p>You can vote!</p>
        {% endif %}
        {% if perms.foo.can_drive %}
            <p>You can drive!</p>
        {% endif %}
    {% else %}
        <p>You don't have permission to do anything in the foo app.</p>
    {% endif %}

Groups
======

Groups are a generic way of categorizing users so you can apply permissions, or
some other label, to those users. A user can belong to any number of groups.

A user in a group automatically has the permissions granted to that group. For
example, if the group ``Site editors`` has the permission
``can_edit_home_page``, any user in that group will have that permission.

Beyond permissions, groups are a convenient way to categorize users to give
them some label, or extended functionality. For example, you could create a
group ``'Special users'``, and you could write code that could, say, give them
access to a members-only portion of your site, or send them members-only e-mail
messages.

Messages
========

.. deprecated:: 1.2
   This functionality will be removed in Django 1.4.  You should use the
   :doc:`messages framework </ref/contrib/messages>` for all new projects and
   begin to update your existing code immediately.

The message system is a lightweight way to queue messages for given users.

A message is associated with a :class:`~django.contrib.auth.models.User`.
There's no concept of expiration or timestamps.

Messages are used by the Django admin after successful actions. For example,
``"The poll Foo was created successfully."`` is a message.

The API is simple:

.. method:: models.User.message_set.create(message)

    To create a new message, use
    ``user_obj.message_set.create(message='message_text')``.

    To retrieve/delete messages, use
    :meth:`user_obj.get_and_delete_messages() <django.contrib.auth.models.User.get_and_delete_messages>`,
    which returns a list of ``Message`` objects in the user's queue (if any)
    and deletes the messages from the queue.

In this example view, the system saves a message for the user after creating
a playlist::

    def create_playlist(request, songs):
        # Create the playlist with the given songs.
        # ...
        request.user.message_set.create(message="Your playlist was added successfully.")
        return render_to_response("playlists/create.html",
            context_instance=RequestContext(request))

When you use :class:`~django.template.context.RequestContext`, the currently
logged-in user and his/her messages are made available in the
:doc:`template context </ref/templates/api>` as the template variable
``{{ messages }}``. Here's an example of template code that displays messages:

.. code-block:: html+django

    {% if messages %}
    <ul>
        {% for message in messages %}
        <li>{{ message }}</li>
        {% endfor %}
    </ul>
    {% endif %}

.. versionchanged:: 1.2
   The ``messages`` template variable uses a backwards compatible method in the
   :doc:`messages framework </ref/contrib/messages>` to retrieve messages from
   both the user ``Message`` model and from the new framework.  Unlike in
   previous revisions, the messages will not be erased unless they are actually
   displayed.

Finally, note that this messages framework only works with users in the user
database. To send messages to anonymous users, use the
:doc:`messages framework </ref/contrib/messages>`.

.. _authentication-backends:

Other authentication sources
============================

The authentication that comes with Django is good enough for most common cases,
but you may have the need to hook into another authentication source -- that
is, another source of usernames and passwords or authentication methods.

For example, your company may already have an LDAP setup that stores a username
and password for every employee. It'd be a hassle for both the network
administrator and the users themselves if users had separate accounts in LDAP
and the Django-based applications.

So, to handle situations like this, the Django authentication system lets you
plug in other authentication sources. You can override Django's default
database-based scheme, or you can use the default system in tandem with other
systems.

See the :doc:`authentication backend reference </ref/authbackends>`
for information on the authentication backends included with Django.

Specifying authentication backends
----------------------------------

Behind the scenes, Django maintains a list of "authentication backends" that it
checks for authentication. When somebody calls
:func:`django.contrib.auth.authenticate()` -- as described in :ref:`How to log
a user in <how-to-log-a-user-in>` above -- Django tries authenticating across
all of its authentication backends. If the first authentication method fails,
Django tries the second one, and so on, until all backends have been attempted.

The list of authentication backends to use is specified in the
:setting:`AUTHENTICATION_BACKENDS` setting. This should be a tuple of Python
path names that point to Python classes that know how to authenticate. These
classes can be anywhere on your Python path.

By default, :setting:`AUTHENTICATION_BACKENDS` is set to::

    ('django.contrib.auth.backends.ModelBackend',)

That's the basic authentication scheme that checks the Django users database.

The order of :setting:`AUTHENTICATION_BACKENDS` matters, so if the same
username and password is valid in multiple backends, Django will stop
processing at the first positive match.

.. note::

    Once a user has authenticated, Django stores which backend was used to
    authenticate the user in the user's session, and re-uses the same backend
    for subsequent authentication attempts for that user. This effectively means
    that authentication sources are cached, so if you change
    :setting:`AUTHENTICATION_BACKENDS`, you'll need to clear out session data if
    you need to force users to re-authenticate using different methods. A simple
    way to do that is simply to execute ``Session.objects.all().delete()``.

Writing an authentication backend
---------------------------------

An authentication backend is a class that implements two methods:
``get_user(user_id)`` and ``authenticate(**credentials)``.

The ``get_user`` method takes a ``user_id`` -- which could be a username,
database ID or whatever -- and returns a ``User`` object.

The ``authenticate`` method takes credentials as keyword arguments. Most of
the time, it'll just look like this::

    class MyBackend:
        def authenticate(self, username=None, password=None):
            # Check the username/password and return a User.

But it could also authenticate a token, like so::

    class MyBackend:
        def authenticate(self, token=None):
            # Check the token and return a User.

Either way, ``authenticate`` should check the credentials it gets, and it
should return a ``User`` object that matches those credentials, if the
credentials are valid. If they're not valid, it should return ``None``.

The Django admin system is tightly coupled to the Django ``User`` object
described at the beginning of this document. For now, the best way to deal with
this is to create a Django ``User`` object for each user that exists for your
backend (e.g., in your LDAP directory, your external SQL database, etc.) You
can either write a script to do this in advance, or your ``authenticate``
method can do it the first time a user logs in.

Here's an example backend that authenticates against a username and password
variable defined in your ``settings.py`` file and creates a Django ``User``
object the first time a user authenticates::

    from django.conf import settings
    from django.contrib.auth.models import User, check_password

    class SettingsBackend:
        """
        Authenticate against the settings ADMIN_LOGIN and ADMIN_PASSWORD.

        Use the login name, and a hash of the password. For example:

        ADMIN_LOGIN = 'admin'
        ADMIN_PASSWORD = 'sha1$4e987$afbcf42e21bd417fb71db8c66b321e9fc33051de'
        """

        supports_object_permissions = False
        supports_anonymous_user = False
        supports_inactive_user = False

        def authenticate(self, username=None, password=None):
            login_valid = (settings.ADMIN_LOGIN == username)
            pwd_valid = check_password(password, settings.ADMIN_PASSWORD)
            if login_valid and pwd_valid:
                try:
                    user = User.objects.get(username=username)
                except User.DoesNotExist:
                    # Create a new user. Note that we can set password
                    # to anything, because it won't be checked; the password
                    # from settings.py will.
                    user = User(username=username, password='get from settings.py')
                    user.is_staff = True
                    user.is_superuser = True
                    user.save()
                return user
            return None

        def get_user(self, user_id):
            try:
                return User.objects.get(pk=user_id)
            except User.DoesNotExist:
                return None

Handling authorization in custom backends
-----------------------------------------

Custom auth backends can provide their own permissions.

The user model will delegate permission lookup functions
(:meth:`~django.contrib.auth.models.User.get_group_permissions()`,
:meth:`~django.contrib.auth.models.User.get_all_permissions()`,
:meth:`~django.contrib.auth.models.User.has_perm()`, and
:meth:`~django.contrib.auth.models.User.has_module_perms()`) to any
authentication backend that implements these functions.

The permissions given to the user will be the superset of all permissions
returned by all backends. That is, Django grants a permission to a user that
any one backend grants.

The simple backend above could implement permissions for the magic admin
fairly simply::

    class SettingsBackend:

        # ...

        def has_perm(self, user_obj, perm):
            if user_obj.username == settings.ADMIN_LOGIN:
                return True
            else:
                return False

This gives full permissions to the user granted access in the above example.
Notice that the backend auth functions all take the user object as an argument,
and they also accept the same arguments given to the associated
:class:`django.contrib.auth.models.User` functions.

A full authorization implementation can be found in
`django/contrib/auth/backends.py`_, which is the default backend and queries
the ``auth_permission`` table most of the time.

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

Authorization for anonymous users
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. versionchanged:: 1.2

An anonymous user is one that is not authenticated i.e. they have provided no
valid authentication details. However, that does not necessarily mean they are
not authorized to do anything. At the most basic level, most Web sites
authorize anonymous users to browse most of the site, and many allow anonymous
posting of comments etc.

Django's permission framework does not have a place to store permissions for
anonymous users. However, it has a foundation that allows custom authentication
backends to specify authorization for anonymous users. This is especially useful
for the authors of re-usable apps, who can delegate all questions of authorization
to the auth backend, rather than needing settings, for example, to control
anonymous access.

To enable this in your own backend, you must set the class attribute
``supports_anonymous_user`` to ``True``. (This precaution is to maintain
compatibility with backends that assume that all user objects are actual
instances of the :class:`django.contrib.auth.models.User` class). With this
in place, :class:`django.contrib.auth.models.AnonymousUser` will delegate all
the relevant permission methods to the authentication backends.

A nonexistent ``supports_anonymous_user`` attribute will raise a hidden
``PendingDeprecationWarning`` if used in Django 1.2. In Django 1.3, this
warning will be upgraded to a ``DeprecationWarning``, which will be displayed
loudly. Additionally ``supports_anonymous_user`` will be set to ``False``.
Django 1.4 will assume that every backend supports anonymous users being
passed to the authorization methods.

Authorization for inactive users
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. versionadded:: 1.3

An inactive user is a one that is authenticated but has its attribute
``is_active`` set to ``False``. However this does not mean they are not
authorized to do anything. For example they are allowed to activate their
account.

The support for anonymous users in the permission system allows for
anonymous users to have permissions to do something while inactive
authenticated users do not.

To enable this on your own backend, you must set the class attribute
``supports_inactive_user`` to ``True``.

A nonexisting ``supports_inactive_user`` attribute will raise a
``PendingDeprecationWarning`` if used in Django 1.3. In Django 1.4, this
warning will be updated to a ``DeprecationWarning`` which will be displayed
loudly. Additionally ``supports_inactive_user`` will be set to ``False``.
Django 1.5 will assume that every backend supports inactive users being
passed to the authorization methods.


Handling object permissions
---------------------------

Django's permission framework has a foundation for object permissions, though
there is no implementation for it in the core. That means that checking for
object permissions will always return ``False`` or an empty list (depending on
the check performed).

To enable object permissions in your own
:doc:`authentication backend </ref/authbackends>` you'll just have
to allow passing an ``obj`` parameter to the permission methods and set the
``supports_object_permissions`` class attribute to ``True``.

A nonexistent ``supports_object_permissions`` will raise a hidden
``PendingDeprecationWarning`` if used in Django 1.2. In Django 1.3, this
warning will be upgraded to a ``DeprecationWarning``, which will be displayed
loudly. Additionally ``supports_object_permissions`` will be set to ``False``.
Django 1.4 will assume that every backend supports object permissions and
won't check for the existence of ``supports_object_permissions``, which
means not supporting ``obj`` as a parameter will raise a ``TypeError``.