customizing.txt

====================================
Customizing authentication in Django
====================================

The authentication that comes with Django is good enough for most common cases,
but you may have needs not met by the out-of-the-box defaults. To customize
authentication to your projects needs involves understanding what points of the
provided system are extendible or replaceable. This document provides details
about how the auth system can be customized.

:ref:`Authentication backends <authentication-backends>` provide an extensible
system for when a username and password stored with the User model need
to be authenticated against a different service than Django's default.

You can give your models :ref:`custom permissions <custom-permissions>` that can be
checked through Django's authorization system.

You can :ref:`extend <extending-user>` the default User model, or :ref:`substitute
<auth-custom-user>` a completely customized model.

.. _authentication-backends:

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

There may be times you 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 :ref:`authentication backend reference
<authentication-backends-reference>` 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 backend that checks the Django users database
and queries the built-in permissions. It does not provide protection against
brute force attacks via any rate limiting mechanism. You may either implement
your own rate limiting mechanism in a custom auth backend, or use the
mechanisms provided by most Web servers.

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 the duration of that session whenever access to the currently
    authenticated user is needed. This effectively means that authentication
    sources are cached on a per-session basis, 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()``.

.. versionadded:: 1.6

    If a backend raises a :class:`~django.core.exceptions.PermissionDenied`
    exception, authentication will immediately fail. Django won't check the
    backends that follow.

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

An authentication backend is a class that implements two required methods:
``get_user(user_id)`` and ``authenticate(**credentials)``, as well as a set of
optional permission related :ref:`authorization methods <authorization_methods>`.

The ``get_user`` method takes a ``user_id`` -- which could be a username,
database ID or whatever, but has to be the primary key of your ``User`` object
-- 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(object):
        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(object):
        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(object):
        """
        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'
        """

        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

.. _authorization_methods:

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(object):
        ...
        def has_perm(self, user_obj, perm, obj=None):
            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 in addition to the same arguments given to the associated
:class:`django.contrib.auth.models.User` functions, the backend auth functions
all take the user object, which may be an anonymous user, as an argument.

A full authorization implementation can be found in the ``ModelBackend`` class
in `django/contrib/auth/backends.py`_, which is the default backend and queries
the ``auth_permission`` table most of the time. If you wish to provide
custom behavior for only part of the backend API, you can take advantage of
Python inheritance and subclass ``ModelBackend`` instead of implementing the
complete API in a custom backend.

.. _django/contrib/auth/backends.py: https://github.com/django/django/blob/master/django/contrib/auth/backends.py

.. _anonymous_auth:

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

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, the user object passed to an authentication backend
may be an :class:`django.contrib.auth.models.AnonymousUser` object, allowing
the backend to specify custom authorization behavior 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.

.. _inactive_auth:

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

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 a scenario
where anonymous users have permissions to do something while inactive
authenticated users do not.

Do not forget to test for the ``is_active`` attribute of the user in your own
backend permission 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). An authentication backend will receive the keyword
parameters ``obj`` and ``user_obj`` for each object related authorization
method and can return the object level permission as appropriate.

.. _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 application::

    class Task(models.Model):
        ...
        class Meta:
            permissions = (
                ("view_task", "Can see available tasks"),
                ("change_task_status", "Can change the status of tasks"),
                ("close_task", "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.) Continuing the above example, the following checks if a user may
view tasks::

    user.has_perm('app.view_task')

.. _extending-user:

Extending the existing User model
=================================

There are two ways to extend the default
:class:`~django.contrib.auth.models.User` model without substituting your own
model. If the changes you need are purely behavioral, and don't require any
change to what is stored in the database, you can create a :ref:`proxy model
<proxy-models>` based on :class:`~django.contrib.auth.models.User`. This
allows for any of the features offered by proxy models including default
ordering, custom managers, or custom model methods.

If you wish to store information related to ``User``, you can use a :ref:`one-to-one
relationship <ref-onetoone>` to a model containing the fields for
additional information. This one-to-one model is often called a profile model,
as it might store non-auth related information about a site user. For example
you might create an Employee model::

    from django.contrib.auth.models import User

    class Employee(models.Model):
        user = models.OneToOneField(User)
        department = models.CharField(max_length=100)

Assuming an existing Employee Fred Smith who has both a User and Employee
model, you can access the related information using Django's standard related
model conventions::

    >>> u = User.objects.get(username='fsmith')
    >>> freds_department = u.employee.department

To add a profile model's fields to the user page in the admin, define an
:class:`~django.contrib.admin.InlineModelAdmin` (for this example, we'll use a
:class:`~django.contrib.admin.StackedInline`) in your app's ``admin.py`` and
add it to a ``UserAdmin`` class which is registered with the
:class:`~django.contrib.auth.models.User` class::

    from django.contrib import admin
    from django.contrib.auth.admin import UserAdmin
    from django.contrib.auth.models import User

    from my_user_profile_app.models import Employee

    # Define an inline admin descriptor for Employee model
    # which acts a bit like a singleton
    class EmployeeInline(admin.StackedInline):
        model = Employee
        can_delete = False
        verbose_name_plural = 'employee'

    # Define a new User admin
    class UserAdmin(UserAdmin):
        inlines = (EmployeeInline, )

    # Re-register UserAdmin
    admin.site.unregister(User)
    admin.site.register(User, UserAdmin)

These profile models are not special in any way - they are just Django models that
happen to have a one-to-one link with a User model. As such, they do not get
auto created when a user is created, but
a :attr:`django.db.models.signals.post_save` could be used to create or update
related models as appropriate.

Note that using related models results in additional queries or joins to
retrieve the related data, and depending on your needs substituting the User
model and adding the related fields may be your better option.  However
existing links to the default User model within your project's apps may justify
the extra database load.

.. _auth-custom-user:

Substituting a custom User model
================================

.. versionadded:: 1.5

Some kinds of projects may have authentication requirements for which Django's
built-in :class:`~django.contrib.auth.models.User` model is not always
appropriate. For instance, on some sites it makes more sense to use an email
address as your identification token instead of a username.

Django allows you to override the default User model by providing a value for
the :setting:`AUTH_USER_MODEL` setting that references a custom model::

     AUTH_USER_MODEL = 'myapp.MyUser'

This dotted pair describes the name of the Django app (which must be in your
:setting:`INSTALLED_APPS`), and the name of the Django model that you wish to
use as your User model.

.. warning::

   Changing :setting:`AUTH_USER_MODEL` has a big effect on your database
   structure. It changes the tables that are available, and it will affect the
   construction of foreign keys and many-to-many relationships. If you intend
   to set :setting:`AUTH_USER_MODEL`, you should set it before running
   ``manage.py syncdb`` for the first time.

   If you have an existing project and you want to migrate to using a custom
   User model, you may need to look into using a migration tool like South_
   to ease the transition.

.. _South: http://south.aeracode.org

Referencing the User model
--------------------------

.. currentmodule:: django.contrib.auth

If you reference :class:`~django.contrib.auth.models.User` directly (for
example, by referring to it in a foreign key), your code will not work in
projects where the :setting:`AUTH_USER_MODEL` setting has been changed to a
different User model.

.. function:: get_user_model()

    Instead of referring to :class:`~django.contrib.auth.models.User` directly,
    you should reference the user model using
    ``django.contrib.auth.get_user_model()``. This method will return the
    currently active User model -- the custom User model if one is specified, or
    :class:`~django.contrib.auth.models.User` otherwise.

    When you define a foreign key or many-to-many relations to the User model,
    you should specify the custom model using the :setting:`AUTH_USER_MODEL`
    setting. For example::

        from django.conf import settings
        from django.db import models

        class Article(models.Model):
            author = models.ForeignKey(settings.AUTH_USER_MODEL)

Specifying a custom User model
------------------------------

.. admonition:: Model design considerations

    Think carefully before handling information not directly related to
    authentication in your custom User Model.

    It may be better to store app-specific user information in a model
    that has a relation with the User model. That allows each app to specify
    its own user data requirements without risking conflicts with other
    apps. On the other hand, queries to retrieve this related information
    will involve a database join, which may have an effect on performance.

Django expects your custom User model to meet some minimum requirements.

1. Your model must have an integer primary key.

2. Your model must have a single unique field that can be used for
   identification purposes. This can be a username, an email address,
   or any other unique attribute.

3. Your model must provide a way to address the user in a "short" and
   "long" form. The most common interpretation of this would be to use
   the user's given name as the "short" identifier, and the user's full
   name as the "long" identifier. However, there are no constraints on
   what these two methods return - if you want, they can return exactly
   the same value.

The easiest way to construct a compliant custom User model is to inherit from
:class:`~django.contrib.auth.models.AbstractBaseUser`.
:class:`~django.contrib.auth.models.AbstractBaseUser` provides the core
implementation of a ``User`` model, including hashed passwords and tokenized
password resets. You must then provide some key implementation details:

.. currentmodule:: django.contrib.auth

.. class:: models.CustomUser

    .. attribute:: USERNAME_FIELD

        A string describing the name of the field on the User model that is
        used as the unique identifier. This will usually be a username of
        some kind, but it can also be an email address, or any other unique
        identifier. The field *must* be unique (i.e., have ``unique=True``
        set in its definition).

        In the following example, the field ``identifier`` is used
        as the identifying field::

            class MyUser(AbstractBaseUser):
                identifier = models.CharField(max_length=40, unique=True, db_index=True)
                ...
                USERNAME_FIELD = 'identifier'

    .. attribute:: REQUIRED_FIELDS

        A list of the field names that *must* be provided when creating a user
        via the :djadmin:`createsuperuser` management command. The user will be
        prompted to supply a value for each of these fields. It should include
        any field for which :attr:`~django.db.models.Field.blank` is ``False``
        or undefined, but may include additional fields you want prompted for
        when a user is created interactively. However, it will not work for
        :class:`~django.db.models.ForeignKey` fields.

        For example, here is the partial definition for a ``User`` model that
        defines two required fields - a date of birth and height::

            class MyUser(AbstractBaseUser):
                ...
                date_of_birth = models.DateField()
                height = models.FloatField()
                ...
                REQUIRED_FIELDS = ['date_of_birth', 'height']

        .. note::

            ``REQUIRED_FIELDS`` must contain all required fields on your User
            model, but should *not* contain the ``USERNAME_FIELD``.

    .. attribute:: is_active

        A boolean attribute that indicates whether the user is considered
        "active".  This attribute is provided as an attribute on
        ``AbstractBaseUser`` defaulting to ``True``. How you choose to
        implement it will depend on the details of your chosen auth backends.
        See the documentation of the :attr:`attribute on the builtin user model
        <django.contrib.auth.models.User.is_active>` for details.

    .. method:: get_full_name()

        A longer formal identifier for the user. A common interpretation
        would be the full name name of the user, but it can be any string that
        identifies the user.

    .. method:: get_short_name()

        A short, informal identifier for the user. A common interpretation
        would be the first name of the user, but it can be any string that
        identifies the user in an informal way. It may also return the same
        value as :meth:`django.contrib.auth.models.User.get_full_name()`.

The following methods are available on any subclass of
:class:`~django.contrib.auth.models.AbstractBaseUser`:

.. class:: models.AbstractBaseUser

    .. method:: get_username()

        Returns the value of the field nominated by ``USERNAME_FIELD``.

    .. method:: models.AbstractBaseUser.is_anonymous()

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

    .. method:: models.AbstractBaseUser.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.AbstractBaseUser.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.AbstractBaseUser` object.

        When the raw_password is ``None``, the password will be set to an
        unusable password, as if
        :meth:`~django.contrib.auth.models.AbstractBaseUser.set_unusable_password()`
        were used.

        .. versionchanged:: 1.6

            In Django 1.4 and 1.5, a blank string was unintentionally stored
            as an unsable password as well.

    .. method:: models.AbstractBaseUser.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.)

        .. versionchanged:: 1.6

            In Django 1.4 and 1.5, a blank string was unintentionally
            considered to be an unusable password, resulting in this method
            returning ``False`` for such a password.

    .. method:: models.AbstractBaseUser.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.AbstractBaseUser.check_password()` for this user
        will never return ``True``. Doesn't save the
        :class:`~django.contrib.auth.models.AbstractBaseUser` object.

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

    .. method:: models.AbstractBaseUser.has_usable_password()

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

You should also define a custom manager for your ``User`` model. If your
``User`` model defines ``username`` and ``email`` fields the same as Django's
default ``User``, you can just install Django's
:class:`~django.contrib.auth.models.UserManager`; however, if your ``User``
model defines different fields, you will need to define a custom manager that
extends :class:`~django.contrib.auth.models.BaseUserManager` providing two
additional methods:

.. class:: models.CustomUserManager

    .. method:: models.CustomUserManager.create_user(*username_field*, password=None, \**other_fields)

        The prototype of ``create_user()`` should accept the username field,
        plus all required fields as arguments. For example, if your user model
        uses ``email`` as the username field, and has ``date_of_birth`` as a
        required fields, then ``create_user`` should be defined as::

            def create_user(self, email, date_of_birth, password=None):
                # create user here
                ...

    .. method:: models.CustomUserManager.create_superuser(*username_field*, password, \**other_fields)

        The prototype of ``create_superuser()`` should accept the username
        field, plus all required fields as arguments. For example, if your user
        model uses ``email`` as the username field, and has ``date_of_birth``
        as a required fields, then ``create_superuser`` should be defined as::

            def create_superuser(self, email, date_of_birth, password):
                # create superuser here
                ...

        Unlike ``create_user()``, ``create_superuser()`` *must* require the
        caller to provider a password.

:class:`~django.contrib.auth.models.BaseUserManager` provides the following
utility methods:

.. class:: models.BaseUserManager

    .. method:: models.BaseUserManager.normalize_email(email)

        A classmethod that normalizes email addresses by lowercasing
        the domain portion of the email address.

    .. method:: models.BaseUserManager.get_by_natural_key(username)

        Retrieves a user instance using the contents of the field
        nominated by ``USERNAME_FIELD``.

    .. method:: models.BaseUserManager.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)

Extending Django's default User
-------------------------------

If you're entirely happy with Django's :class:`~django.contrib.auth.models.User`
model and you just want to add some additional profile information, you can
simply subclass ``django.contrib.auth.models.AbstractUser`` and add your
custom profile fields. This class provides the full implementation of the
default :class:`~django.contrib.auth.models.User` as an :ref:`abstract model
<abstract-base-classes>`.

.. _custom-users-and-the-built-in-auth-forms:

Custom users and the built-in auth forms
----------------------------------------

As you may expect, built-in Django's :ref:`forms <built-in-auth-forms>` and
:ref:`views <built-in-auth-views>` make certain assumptions about the user
model that they are working with.

If your user model doesn't follow the same assumptions, it may be necessary to define
a replacement form, and pass that form in as part of the configuration of the
auth views.

* :class:`~django.contrib.auth.forms.UserCreationForm`

  Depends on the :class:`~django.contrib.auth.models.User` model.
  Must be re-written for any custom user model.

* :class:`~django.contrib.auth.forms.UserChangeForm`

  Depends on the :class:`~django.contrib.auth.models.User` model.
  Must be re-written for any custom user model.

* :class:`~django.contrib.auth.forms.AuthenticationForm`

  Works with any subclass of :class:`~django.contrib.auth.models.AbstractBaseUser`,
  and will adapt to use the field defined in `USERNAME_FIELD`.

* :class:`~django.contrib.auth.forms.PasswordResetForm`

  Assumes that the user model has an integer primary key, has a field named
  ``email`` that can be used to identify the user, and a boolean field
  named `is_active` to prevent password resets for inactive users.

* :class:`~django.contrib.auth.forms.SetPasswordForm`

  Works with any subclass of :class:`~django.contrib.auth.models.AbstractBaseUser`

* :class:`~django.contrib.auth.forms.PasswordChangeForm`

  Works with any subclass of :class:`~django.contrib.auth.models.AbstractBaseUser`

* :class:`~django.contrib.auth.forms.AdminPasswordChangeForm`

  Works with any subclass of :class:`~django.contrib.auth.models.AbstractBaseUser`


Custom users and :mod:`django.contrib.admin`
--------------------------------------------

If you want your custom User model to also work with Admin, your User model must
define some additional attributes and methods. These methods allow the admin to
control access of the User to admin content:

.. class:: models.CustomUser

.. attribute:: is_staff

    Returns ``True`` if the user is allowed to have access to the admin site.

.. attribute:: is_active

    Returns ``True`` if the user account is currently active.

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

    Returns ``True`` if the user has the named permission. If ``obj`` is
    provided, the permission needs to be checked against a specific object
    instance.

.. method:: has_module_perms(app_label):

    Returns ``True`` if the user has permission to access models in
    the given app.

You will also need to register your custom User model with the admin. If
your custom User model extends ``django.contrib.auth.models.AbstractUser``,
you can use Django's existing ``django.contrib.auth.admin.UserAdmin``
class. However, if your User model extends
:class:`~django.contrib.auth.models.AbstractBaseUser`, you'll need to define
a custom ModelAdmin class. It may be possible to subclass the default
``django.contrib.auth.admin.UserAdmin``; however, you'll need to
override any of the definitions that refer to fields on
``django.contrib.auth.models.AbstractUser`` that aren't on your
custom User class.

Custom users and permissions
----------------------------

To make it easy to include Django's permission framework into your own User
class, Django provides :class:`~django.contrib.auth.models.PermissionsMixin`.
This is an abstract model you can include in the class hierarchy for your User
model, giving you all the methods and database fields necessary to support
Django's permission model.

:class:`~django.contrib.auth.models.PermissionsMixin` provides the following
methods and attributes:

.. class:: models.PermissionsMixin

    .. attribute:: models.PermissionsMixin.is_superuser

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

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

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

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

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

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

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

    .. method:: models.PermissionsMixin.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
        :ref:`permissions <topic-authorization>`). If the user is inactive, this method will
        always return ``False``.

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

    .. method:: models.PermissionsMixin.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``.

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

    .. method:: models.PermissionsMixin.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``.

.. admonition:: ModelBackend

    If you don't include the
    :class:`~django.contrib.auth.models.PermissionsMixin`, you must ensure you
    don't invoke the permissions methods on ``ModelBackend``. ``ModelBackend``
    assumes that certain fields are available on your user model. If your User
    model doesn't provide  those fields, you will receive database errors when
    you check permissions.

Custom users and Proxy models
-----------------------------

One limitation of custom User models is that installing a custom User model
will break any proxy model extending :class:`~django.contrib.auth.models.User`.
Proxy models must be based on a concrete base class; by defining a custom User
model, you remove the ability of Django to reliably identify the base class.

If your project uses proxy models, you must either modify the proxy to extend
the User model that is currently in use in your project, or merge your proxy's
behavior into your User subclass.

Custom users and signals
------------------------

Another limitation of custom User models is that you can't use
:func:`django.contrib.auth.get_user_model()` as the sender or target of a signal
handler. Instead, you must register the handler with the resulting User model.
See :doc:`/topics/signals` for more information on registering an sending
signals.

Custom users and testing/fixtures
---------------------------------

If you are writing an application that interacts with the User model, you must
take some precautions to ensure that your test suite will run regardless of
the User model that is being used by a project. Any test that instantiates an
instance of User will fail if the User model has been swapped out. This
includes any attempt to create an instance of User with a fixture.

To ensure that your test suite will pass in any project configuration,
``django.contrib.auth.tests.utils`` defines a ``@skipIfCustomUser`` decorator.
This decorator will cause a test case to be skipped if any User model other
than the default Django user is in use. This decorator can be applied to a
single test, or to an entire test class.

Depending on your application, tests may also be needed to be added to ensure
that the application works with *any* user model, not just the default User
model. To assist with this, Django provides two substitute user models that
can be used in test suites:

* ``django.contrib.auth.tests.custom_user.CustomUser``, a custom user
  model that uses an ``email`` field as the username, and has a basic
  admin-compliant permissions setup

* ``django.contrib.auth.tests.custom_user.ExtensionUser``, a custom
  user model that extends ``django.contrib.auth.models.AbstractUser``,
  adding a ``date_of_birth`` field.

You can then use the ``@override_settings`` decorator to make that test run
with the custom User model. For example, here is a skeleton for a test that
would test three possible User models -- the default, plus the two User
models provided by ``auth`` app::

    from django.contrib.auth.tests.utils import skipIfCustomUser
    from django.test import TestCase
    from django.test.utils import override_settings


    class ApplicationTestCase(TestCase):
        @skipIfCustomUser
        def test_normal_user(self):
            "Run tests for the normal user model"
            self.assertSomething()

        @override_settings(AUTH_USER_MODEL='auth.CustomUser')
        def test_custom_user(self):
            "Run tests for a custom user model with email-based authentication"
            self.assertSomething()

        @override_settings(AUTH_USER_MODEL='auth.ExtensionUser')
        def test_extension_user(self):
            "Run tests for a simple extension of the built-in User."
            self.assertSomething()


A full example
--------------

Here is an example of an admin-compliant custom user app. This user model uses
an email address as the username, and has a required date of birth; it
provides no permission checking, beyond a simple ``admin`` flag on the user
account. This model would be compatible with all the built-in auth forms and
views, except for the User creation forms. This example illustrates how most of
the components work together, but is not intended to be copied directly into
projects for production use.

This code would all live in a ``models.py`` file for a custom
authentication app::

    from django.db import models
    from django.contrib.auth.models import (
        BaseUserManager, AbstractBaseUser
    )


    class MyUserManager(BaseUserManager):
        def create_user(self, email, date_of_birth, password=None):
            """
            Creates and saves a User with the given email, date of
            birth and password.
            """
            if not email:
                raise ValueError('Users must have an email address')

            user = self.model(
                email=self.normalize_email(email),
                date_of_birth=date_of_birth,
            )

            user.set_password(password)
            user.save(using=self._db)
            return user

        def create_superuser(self, email, date_of_birth, password):
            """
            Creates and saves a superuser with the given email, date of
            birth and password.
            """
            user = self.create_user(email,
                password=password,
                date_of_birth=date_of_birth
            )
            user.is_admin = True
            user.save(using=self._db)
            return user


    class MyUser(AbstractBaseUser):
        email = models.EmailField(
            verbose_name='email address',
            max_length=255,
            unique=True,
            db_index=True,
        )
        date_of_birth = models.DateField()
        is_active = models.BooleanField(default=True)
        is_admin = models.BooleanField(default=False)

        objects = MyUserManager()

        USERNAME_FIELD = 'email'
        REQUIRED_FIELDS = ['date_of_birth']

        def get_full_name(self):
            # The user is identified by their email address
            return self.email

        def get_short_name(self):
            # The user is identified by their email address
            return self.email

        # On Python 3: def __str__(self):
        def __unicode__(self):
            return self.email

        def has_perm(self, perm, obj=None):
            "Does the user have a specific permission?"
            # Simplest possible answer: Yes, always
            return True

        def has_module_perms(self, app_label):
            "Does the user have permissions to view the app `app_label`?"
            # Simplest possible answer: Yes, always
            return True

        @property
        def is_staff(self):
            "Is the user a member of staff?"
            # Simplest possible answer: All admins are staff
            return self.is_admin

Then, to register this custom User model with Django's admin, the following
code would be required in the app's ``admin.py`` file::

    from django import forms
    from django.contrib import admin
    from django.contrib.auth.models import Group
    from django.contrib.auth.admin import UserAdmin
    from django.contrib.auth.forms import ReadOnlyPasswordHashField

    from customauth.models import MyUser


    class UserCreationForm(forms.ModelForm):
        """A form for creating new users. Includes all the required
        fields, plus a repeated password."""
        password1 = forms.CharField(label='Password', widget=forms.PasswordInput)
        password2 = forms.CharField(label='Password confirmation', widget=forms.PasswordInput)

        class Meta:
            model = MyUser
            fields = ('email', 'date_of_birth')

        def clean_password2(self):
            # Check that the two password entries match
            password1 = self.cleaned_data.get("password1")
            password2 = self.cleaned_data.get("password2")
            if password1 and password2 and password1 != password2:
                raise forms.ValidationError("Passwords don't match")
            return password2

        def save(self, commit=True):
            # Save the provided password in hashed format
            user = super(UserCreationForm, self).save(commit=False)
            user.set_password(self.cleaned_data["password1"])
            if commit:
                user.save()
            return user


    class UserChangeForm(forms.ModelForm):
        """A form for updating users. Includes all the fields on
        the user, but replaces the password field with admin's
        password hash display field.
        """
        password = ReadOnlyPasswordHashField()

        class Meta:
            model = MyUser
            fields = ['email', 'password', 'date_of_birth', 'is_active', 'is_admin']

        def clean_password(self):
            # Regardless of what the user provides, return the initial value.
            # This is done here, rather than on the field, because the
            # field does not have access to the initial value
            return self.initial["password"]


    class MyUserAdmin(UserAdmin):
        # The forms to add and change user instances
        form = UserChangeForm
        add_form = UserCreationForm

        # The fields to be used in displaying the User model.
        # These override the definitions on the base UserAdmin
        # that reference specific fields on auth.User.
        list_display = ('email', 'date_of_birth', 'is_admin')
        list_filter = ('is_admin',)
        fieldsets = (
            (None, {'fields': ('email', 'password')}),
            ('Personal info', {'fields': ('date_of_birth',)}),
            ('Permissions', {'fields': ('is_admin',)}),
        )
        add_fieldsets = (
            (None, {
                'classes': ('wide',),
                'fields': ('email', 'date_of_birth', 'password1', 'password2')}
            ),
        )
        search_fields = ('email',)
        ordering = ('email',)
        filter_horizontal = ()

    # Now register the new UserAdmin...
    admin.site.register(MyUser, MyUserAdmin)
    # ... and, since we're not using Django's builtin permissions,
    # unregister the Group model from admin.
    admin.site.unregister(Group)

Finally, specify the custom model as the default user model for your project
using the :setting:`AUTH_USER_MODEL` setting in your ``settings.py``::

    AUTH_USER_MODEL = 'customauth.MyUser'