django/docs/topics/auth/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. Customizing
authentication in your projects requires understanding what points of the
provided system are extensible 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>` -- 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 list 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.

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

.. note::

    Once a user has authenticated, Django stores which backend was used to
    authenticate the user in the user's session, and reuses 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 to execute ``Session.objects.all().delete()``.

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

An authentication backend is a class that implements two required methods:
``get_user(user_id)`` and ``authenticate(request, **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 or ``None``.

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

    from django.contrib.auth.backends import BaseBackend


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

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

    from django.contrib.auth.backends import BaseBackend


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

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

``request`` is an :class:`~django.http.HttpRequest` and may be ``None`` if it
wasn't provided to :func:`~django.contrib.auth.authenticate` (which passes it
on to the backend).

The Django admin is tightly coupled to the Django :ref:`User object
<user-objects>`. For example, for a user to access the admin,
:attr:`.User.is_staff` and :attr:`.User.is_active` must be ``True`` (see
:meth:`.AdminSite.has_permission` for details).

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. In this example, the created Django
``User`` object is a superuser who will have full access to the admin::

    from django.conf import settings
    from django.contrib.auth.backends import BaseBackend
    from django.contrib.auth.hashers import check_password
    from django.contrib.auth.models import User


    class SettingsBackend(BaseBackend):
        """
        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 = 'pbkdf2_sha256$30000$Vo0VlMnkR4Bk$qEvtdyZRWTcOsCnI/oQ7fVOu1XAURIZYoOZ3iq8Dr4M='
        """

        def authenticate(self, request, 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. There's no need to set a password
                    # because only the password from settings.py is checked.
                    user = User(username=username)  # is_active defaults to True.
                    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 and its manager will delegate permission lookup functions
(:meth:`~django.contrib.auth.models.User.get_user_permissions()`,
: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()`,
:meth:`~django.contrib.auth.models.User.has_module_perms()`, and
:meth:`~django.contrib.auth.models.UserManager.with_perm()`) 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.

If a backend raises a :class:`~django.core.exceptions.PermissionDenied`
exception in :meth:`~django.contrib.auth.models.User.has_perm()` or
:meth:`~django.contrib.auth.models.User.has_module_perms()`, the authorization
will immediately fail and Django won't check the backends that follow.

A backend could implement permissions for the magic admin like this::

    from django.contrib.auth.backends import BaseBackend


    class MagicAdminBackend(BaseBackend):
        def has_perm(self, user_obj, perm, obj=None):
            return user_obj.username == settings.ADMIN_LOGIN

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 :source:`django/contrib/auth/backends.py`, which is the default backend and
queries the ``auth_permission`` table most of the time.

.. _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 websites
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 reusable 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 one that has its
:attr:`~django.contrib.auth.models.User.is_active` field set to ``False``. The
:class:`~django.contrib.auth.backends.ModelBackend` and
:class:`~django.contrib.auth.backends.RemoteUserBackend` authentication
backends prohibits these users from authenticating. If a custom user model
doesn't have an :attr:`~django.contrib.auth.models.CustomUser.is_active` field,
all users will be allowed to authenticate.

You can use :class:`~django.contrib.auth.backends.AllowAllUsersModelBackend`
or :class:`~django.contrib.auth.backends.AllowAllUsersRemoteUserBackend` if you
want to allow inactive users to authenticate.

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 two custom permissions, i.e., actions users
can or cannot do with ``Task`` instances, specific to your application::

    class Task(models.Model):
        ...

        class Meta:
            permissions = [
                ("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 migrate <migrate>` (the function that creates permissions
is connected to the :data:`~django.db.models.signals.post_migrate` signal).
Your code is in charge of checking the value of these permissions when a user
is trying to access the functionality provided by the application (changing the
status of tasks or closing tasks.) Continuing the above example, the following
checks if a user may close tasks::

    user.has_perm("app.close_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
:class:`~django.db.models.OneToOneField` 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, on_delete=models.CASCADE)
        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:

.. code-block:: pycon

    >>> 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 as BaseUserAdmin
    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(BaseUserAdmin):
        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 aren't
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.

Using related models results in additional queries or joins to retrieve the
related data. Depending on your needs, a custom user model that includes the
related fields may be your better option, however, existing relations to the
default user model within your project's apps may justify the extra database
load.

.. _auth-custom-user:

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

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 :attr:`~django.apps.AppConfig.label` 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.

Using a custom user model when starting a project
-------------------------------------------------

If you're starting a new project, you can set up a custom user model that
behaves identically to the default user model by subclassing
:class:`~django.contrib.auth.models.AbstractUser`::

    from django.contrib.auth.models import AbstractUser


    class User(AbstractUser):
        pass

Don't forget to point :setting:`AUTH_USER_MODEL` to it. Do this before creating
any migrations or running ``manage.py migrate`` for the first time.

Also, register the model in the app's ``admin.py``::

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

    admin.site.register(User, UserAdmin)

Changing to a custom user model mid-project
-------------------------------------------

Changing :setting:`AUTH_USER_MODEL` after you've created database tables is
possible, but can be complex, since it affects foreign keys and many-to-many
relationships, for example.

This change can't be done automatically and requires manually fixing your
schema, moving your data from the old user table, and possibly manually
reapplying some migrations. See :ticket:`25313` for an outline of the steps.

Due to limitations of Django's dynamic dependency feature for swappable
models, the model referenced by :setting:`AUTH_USER_MODEL` must be created in
the first migration of its app (usually called ``0001_initial``); otherwise,
you'll have dependency issues.

In addition, you may run into a ``CircularDependencyError`` when running your
migrations as Django won't be able to automatically break the dependency loop
due to the dynamic dependency. If you see this error, you should break the loop
by moving the models depended on by your user model into a second migration.
(You can try making two normal models that have a ``ForeignKey`` to each other
and seeing how ``makemigrations`` resolves that circular dependency if you want
to see how it's usually done.)

Reusable apps and ``AUTH_USER_MODEL``
-------------------------------------

Reusable apps shouldn't implement a custom user model. A project may use many
apps, and two reusable apps that implemented a custom user model couldn't be
used together. If you need to store per user information in your app, use
a :class:`~django.db.models.ForeignKey` or
:class:`~django.db.models.OneToOneField` to ``settings.AUTH_USER_MODEL``
as described below.

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,
                on_delete=models.CASCADE,
            )

    When connecting to signals sent by 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.models.signals import post_save


        def post_save_receiver(sender, instance, created, **kwargs):
            pass


        post_save.connect(post_save_receiver, sender=settings.AUTH_USER_MODEL)

    Generally speaking, it's easiest to refer to the user model with the
    :setting:`AUTH_USER_MODEL` setting in code that's executed at import time,
    however, it's also possible to call ``get_user_model()`` while Django
    is importing models, so you could use
    ``models.ForeignKey(get_user_model(), ...)``.

    If your app is tested with multiple user models, using
    ``@override_settings(AUTH_USER_MODEL=...)`` for example, and you cache the
    result of ``get_user_model()`` in a module-level variable, you may need to
    listen to the  :data:`~django.test.signals.setting_changed` signal to clear
    the cache. For example::

        from django.apps import apps
        from django.contrib.auth import get_user_model
        from django.core.signals import setting_changed
        from django.dispatch import receiver


        @receiver(setting_changed)
        def user_model_swapped(*, setting, **kwargs):
            if setting == "AUTH_USER_MODEL":
                apps.clear_cache()
                from myapp import some_module

                some_module.UserModel = get_user_model()

.. _specifying-custom-user-model:

Specifying a custom user model
------------------------------

When you start your project with a custom user model, stop to consider if this
is the right choice for your project.

Keeping all user related information in one model removes the need for
additional or more complex database queries to retrieve related models. On the
other hand, it may be more suitable to store app-specific user information in a
model that has a relation with your custom user model. That allows each app to
specify its own user data requirements without potentially conflicting or
breaking assumptions by other apps. It also means that you would keep your user
model as simple as possible, focused on authentication, and following the
minimum requirements Django expects custom user models to meet.

If you use the default authentication backend, then 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. A non-unique
username field is allowed if you use a custom authentication backend that
can support it.

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 (e.g. have ``unique=True`` set
        in its definition), unless you use a custom authentication backend that
        can support non-unique usernames.

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

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

    .. attribute:: EMAIL_FIELD

        A string describing the name of the email field on the ``User`` model.
        This value is returned by
        :meth:`~models.AbstractBaseUser.get_email_field_name`.

    .. attribute:: REQUIRED_FIELDS

        A list of the field names that will be prompted for 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 must
        include any field for which :attr:`~django.db.models.Field.blank` is
        ``False`` or undefined and may include additional fields you want
        prompted for when a user is created interactively.
        ``REQUIRED_FIELDS`` has no effect in other parts of Django, like
        creating a user in the admin.

        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`` or
            ``password`` as these fields will always be prompted for.

    .. 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:`is_active attribute on the built-in
        user model <django.contrib.auth.models.User.is_active>` for details.

    .. method:: get_full_name()

        Optional. A longer formal identifier for the user such as their full
        name. If implemented, this appears alongside the username in an
        object's history in :mod:`django.contrib.admin`.

    .. method:: get_short_name()

        Optional. A short, informal identifier for the user such as their
        first name. If implemented, this replaces the username in the greeting
        to the user in the header of :mod:`django.contrib.admin`.

    .. admonition:: Importing ``AbstractBaseUser``

        ``AbstractBaseUser`` and ``BaseUserManager`` are importable from
        ``django.contrib.auth.base_user`` so that they can be imported without
        including ``django.contrib.auth`` in :setting:`INSTALLED_APPS`.

The following attributes and 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:: clean()

        Normalizes the username by calling :meth:`normalize_username`. If you
        override this method, be sure to call ``super()`` to retain the
        normalization.

    .. classmethod:: get_email_field_name()

       Returns the name of the email field specified by the
       :attr:`~models.CustomUser.EMAIL_FIELD` attribute. Defaults to
       ``'email'`` if ``EMAIL_FIELD`` isn't specified.

    .. classmethod:: normalize_username(username)

        Applies NFKC Unicode normalization to usernames so that visually
        identical characters with different Unicode code points are considered
        identical.

    .. attribute:: models.AbstractBaseUser.is_authenticated

        Read-only attribute which is always ``True`` (as opposed to
        ``AnonymousUser.is_authenticated`` which is always ``False``).
        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 or has
        a valid session. Even though normally you will check this attribute on
        ``request.user`` to find out whether it has been populated by the
        :class:`~django.contrib.auth.middleware.AuthenticationMiddleware`
        (representing the currently logged-in user), you should know this
        attribute is ``True`` for any :class:`~models.User` instance.

    .. attribute:: models.AbstractBaseUser.is_anonymous

        Read-only attribute which is always ``False``. This is a way of
        differentiating :class:`~models.User` and :class:`~models.AnonymousUser`
        objects. Generally, you should prefer using
        :attr:`~models.User.is_authenticated` to this attribute.

    .. 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.

    .. method:: models.AbstractBaseUser.check_password(raw_password)
    .. method:: models.AbstractBaseUser.acheck_password(raw_password)

        *Asynchronous version*: ``acheck_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.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.

    .. method:: models.AbstractBaseUser.get_session_auth_hash()

        Returns an HMAC of the password field. Used for
        :ref:`session-invalidation-on-password-change`.

    .. method:: models.AbstractBaseUser.get_session_auth_fallback_hash()

        Yields the HMAC of the password field using
        :setting:`SECRET_KEY_FALLBACKS`. Used by ``get_user()``.

:class:`~models.AbstractUser` subclasses :class:`~models.AbstractBaseUser`:

.. class:: models.AbstractUser

    .. method:: clean()

        Normalizes the email by calling
        :meth:`.BaseUserManager.normalize_email`. If you override this method,
        be sure to call ``super()`` to retain the normalization.

Writing a manager for a custom user model
-----------------------------------------

You should also define a custom manager for your user model. If your user model
defines ``username``, ``email``, ``is_staff``, ``is_active``, ``is_superuser``,
``last_login``, and ``date_joined`` fields the same as Django's default user,
you can install Django's :class:`~django.contrib.auth.models.UserManager`;
however, if your user model defines different fields, you'll 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 field, 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=None, **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 field, then ``create_superuser`` should be defined as::

            def create_superuser(self, email, date_of_birth, password=None):
                # create superuser here
                ...

For a :class:`~.ForeignKey` in :attr:`.USERNAME_FIELD` or
:attr:`.REQUIRED_FIELDS`, these methods receive the value of the
:attr:`~.ForeignKey.to_field` (the :attr:`~django.db.models.Field.primary_key`
by default) of an existing instance.

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

.. class:: models.BaseUserManager

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

        Normalizes email addresses by lowercasing the domain portion of the
        email address.

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

        *Asynchronous version*: ``aget_by_natural_key()``

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

        .. versionchanged:: 5.2

            ``aget_by_natural_key()`` method was added.

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

If you're entirely happy with Django's :class:`~django.contrib.auth.models.User`
model, but you want to add some additional profile information, you could
subclass :class:`django.contrib.auth.models.AbstractUser` and add your custom
profile fields, although we'd recommend a separate model as described in
:ref:`specifying-custom-user-model`. ``AbstractUser`` 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
----------------------------------------

Django's built-in :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.

The following forms are compatible with any subclass of
:class:`~django.contrib.auth.models.AbstractBaseUser`:

* :class:`~django.contrib.auth.forms.AuthenticationForm`: Uses the username
  field specified by :attr:`~models.CustomUser.USERNAME_FIELD`.
* :class:`~django.contrib.auth.forms.SetPasswordForm`
* :class:`~django.contrib.auth.forms.PasswordChangeForm`
* :class:`~django.contrib.auth.forms.AdminPasswordChangeForm`

The following forms make assumptions about the user model and can be used as-is
if those assumptions are met:

* :class:`~django.contrib.auth.forms.PasswordResetForm`: Assumes that the user
  model has a field that stores the user's email address with the name returned
  by :meth:`~models.AbstractBaseUser.get_email_field_name` (``email`` by
  default) that can be used to identify the user and a boolean field named
  ``is_active`` to prevent password resets for inactive users.

Finally, the following forms are tied to
:class:`~django.contrib.auth.models.User` and need to be rewritten or extended
to work with a custom user model:

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

If your custom user model is a subclass of ``AbstractUser``, then you can
extend these forms in this manner::

    from django.contrib.auth.forms import UserCreationForm
    from myapp.models import CustomUser


    class CustomUserCreationForm(UserCreationForm):
        class Meta(UserCreationForm.Meta):
            model = CustomUser
            fields = UserCreationForm.Meta.fields + ("custom_field",)

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

If you want your custom user model to also work with the 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
    :noindex:

.. 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.

.. note::

    If you are using a custom ``ModelAdmin`` which is a subclass of
    ``django.contrib.auth.admin.UserAdmin``, then you need to add your custom
    fields to ``fieldsets`` (for fields to be used in editing users) and to
    ``add_fieldsets`` (for fields to be used when creating a user). For
    example::

        from django.contrib.auth.admin import UserAdmin


        class CustomUserAdmin(UserAdmin):
            ...
            fieldsets = UserAdmin.fieldsets + ((None, {"fields": ["custom_field"]}),)
            add_fieldsets = UserAdmin.add_fieldsets + ((None, {"fields": ["custom_field"]}),)

    See :ref:`a full example <custom-users-admin-full-example>` for more
    details.

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_user_permissions(obj=None)

        Returns a set of permission strings that the user has directly.

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

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

        Returns a set of permission strings that the user has, through their
        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 :attr:`.User.is_active`
        and :attr:`~.User.is_superuser` are both ``True``, this method always
        returns ``True``.

        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 :attr:`.User.is_active` and
        :attr:`~.User.is_superuser` are both ``True``, this method always
        returns ``True``.

        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 :attr:`.User.is_active` and
        :attr:`~.User.is_superuser` are both ``True``, this method always
        returns ``True``.

.. admonition:: ``PermissionsMixin`` and ``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'll 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's in use in your project, or merge your proxy's behavior
into your :class:`~django.contrib.auth.models.User` subclass.

.. _custom-users-admin-full-example:

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 an ``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=None):
            """
            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,
        )
        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 __str__(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 as BaseUserAdmin
    from django.contrib.auth.forms import ReadOnlyPasswordHashField
    from django.core.exceptions import ValidationError

    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 ValidationError("Passwords don't match")
            return password2

        def save(self, commit=True):
            # Save the provided password in hashed format
            user = super().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
        disabled password hash display field.
        """

        password = ReadOnlyPasswordHashField()

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


    class UserAdmin(BaseUserAdmin):
        # 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 is not a standard ModelAdmin attribute. UserAdmin
        # overrides get_fieldsets to use this attribute when creating a user.
        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, UserAdmin)
    # ... and, since we're not using Django's built-in 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"

.. _writing-authentication-backends-async-interface:

Adding an async interface
~~~~~~~~~~~~~~~~~~~~~~~~~

.. versionadded:: 5.2

To optimize performance when called from an async context authentication,
backends can implement async versions of each function - ``aget_user(user_id)``
and ``aauthenticate(request, **credentials)``. When an authentication backend
extends ``BaseBackend`` and async versions of these functions are not provided,
they will be automatically synthesized with ``sync_to_async``. This has
:ref:`performance penalties <async_performance>`.

While an async interface is optional, a synchronous interface is always
required. There is no automatic synthesis for a synchronous interface if an
async interface is implemented.

Django's out-of-the-box authentication backends have native async support. If
these native backends are extended take special care to make sure the async
versions of modified functions are modified as well.