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User authentication in Django

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

Overview

The auth system consists of:

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

Installation

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

  1. Put 'django.contrib.auth' in your INSTALLED_APPS setting.
  2. Run the command manage.py syncdb.

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

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

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

Users

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

API reference

Fields

User objects have the following fields:

  • username - Required. 30 characters or fewer. Alphanumeric characters only (letters, digits and underscores).
  • first_name - Optional. 30 characters or fewer.
  • last_name - Optional. 30 characters or fewer.
  • email - Optional. E-mail address.
  • password - Required. A hash of, and metadata about, the password. (Django doesn't store the raw password.) Raw passwords can be arbitrarily long and can contain any character. See the "Passwords" section below.
  • is_staff - Boolean. Designates whether this user can access the admin site.
  • is_active - Boolean. Designates whether this account can be used to log in. Set this flag to False instead of deleting accounts.
  • is_superuser - Boolean. Designates that this user has all permissions without explicitly assigning them.
  • last_login - A datetime of the user's last login. Is set to the current date/time by default.
  • date_joined - A datetime designating when the account was created. Is set to the current date/time by default when the account is created.

Methods

User objects have two many-to-many fields: groups and user_permissions. User objects can access their related objects in the same way as any other Django model?:

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

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

  • is_anonymous() - Always returns False. This is a way of differentiating User and AnonymousUser objects. Generally, you should prefer using is_authenticated() to this method.
  • 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.
  • get_full_name() - Returns the first_name plus the last_name, with a space in between.
  • set_password(raw_password) - Sets the user's password to the given raw string, taking care of the password hashing. Doesn't save the User object.
  • check_password(raw_password) - Returns True if the given raw string is the correct password for the user. (This takes care of the password hashing in making the comparison.)
  • set_unusable_password() - New in Django development version. Marks the user as having no password set. This isn't the same as having a blank string for a password. check_password() for this user will never return True. Doesn't save the User object.

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

  • has_usable_password() - New in Django development version. Returns False if set_unusable_password() has been called for this user.
  • get_group_permissions() - Returns a list of permission strings that the user has, through his/her groups.
  • get_all_permissions() - Returns a list of permission strings that the user has, both through group and user permissions.
  • has_perm(perm) - Returns True if the user has the specified permission, where perm is in the format "package.codename". If the user is inactive, this method will always return False.
  • has_perms(perm_list) - Returns True if the user has each of the specified permissions, where each perm is in the format "package.codename". If the user is inactive, this method will always return False.
  • 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.
  • get_and_delete_messages() - Returns a list of Message objects in the user's queue and deletes the messages from the queue.
  • email_user(subject, message, from_email=None) - Sends an e-mail to the user. If from_email is None, Django uses the DEFAULT_FROM_EMAIL? setting.
  • get_profile() - Returns a site-specific profile for this user. Raises django.contrib.auth.models.SiteProfileNotAvailable if the current site doesn't allow profiles.

Manager functions

The User model has a custom manager that has the following helper functions:

  • create_user(username, email, password=None) - Creates, saves and returns a User. The username, email and password are set as given, and the User gets is_active=True.

If no password is provided, set_unusable_password() will be called.

See _Creating users for example usage.

  • 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 1, I and 0).

Basic usage

Creating users

The most basic way to create users is to use the create_user helper function that comes with Django:

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

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

Changing passwords

Change a password with set_password():

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

Don't set the password attribute directly unless you know what you're doing. This is explained in the next section.

Passwords

The password attribute of a User object is a string in this format:

hashtype$salt$hash

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

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

For example:

sha1$a1976$a36cc8cbf81742a8fb52e221aaeab48ed7f58ab4

The User.set_password() and User.check_password() functions handle the setting and checking of these values behind the scenes.

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

Anonymous users

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

  • id is always None.
  • is_staff and is_superuser are always False.
  • is_active is always True.
  • groups and user_permissions are always empty.
  • is_anonymous() returns True instead of False.
  • is_authenticated() returns False instead of True.
  • has_perm() always returns False.
  • set_password(), check_password(), save(), delete(), set_groups() and set_permissions() raise NotImplementedError.

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

Creating superusers

manage.py syncdb prompts you to create a superuser the first time you run it after adding 'django.contrib.auth' to your INSTALLED_APPS. But if you need to create a superuser after that via the command line, you can use the create_superuser.py utility. Just run this command:

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

Make sure to substitute /path/to/ with the path to the Django codebase on your filesystem.

Authentication in Web requests

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

First, install the SessionMiddleware and AuthenticationMiddleware middlewares by adding them to your MIDDLEWARE_CLASSES setting. See the session documentation? for more information.

Once you have those middlewares installed, you'll be able to access request.user in views. request.user will give you a User object representing the currently logged-in user. If a user isn't currently logged in, request.user will be set to an instance of AnonymousUser (see the previous section). You can tell them apart with is_authenticated(), like so:

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

How to log a user in

Django provides two functions in django.contrib.auth: authenticate() and login().

To authenticate a given username and password, use authenticate(). It takes two keyword arguments, username and password, and it returns a User object if the password is valid for the given username. If the password is invalid, authenticate() returns None. Example:

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

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

This example shows how you might use both authenticate() and login():

from django.contrib.auth import authenticate, login

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

Manually checking a user's password

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

How to log a user out

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

from django.contrib.auth import logout

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

Note that logout() doesn't throw any errors if the user wasn't logged in.

Limiting access to logged-in users

The raw way

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

from django.http import HttpResponseRedirect

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

...or display an error message:

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

The login_required decorator

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

from django.contrib.auth.decorators import login_required

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

Here's an equivalent example, using the more compact decorator syntax introduced in Python 2.4:

from django.contrib.auth.decorators import login_required

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

In the Django development version, login_required also takes an optional redirect_field_name parameter. Example:

from django.contrib.auth.decorators import login_required

def my_view(request):
    # ...
my_view = login_required(redirect_field_name='redirect_to')(my_view)

Again, an equivalent example of the more compact decorator syntax introduced in Python 2.4:

from django.contrib.auth.decorators import login_required

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

login_required does the following:

  • If the user isn't logged in, redirect to settings.LOGIN_URL (/accounts/login/ by default), passing the current absolute URL in the query string as next or the value of redirect_field_name. For example: /accounts/login/?next=/polls/3/.
  • If the user is logged in, execute the view normally. The view code is free to assume the user is logged in.

Note that you'll need to map the appropriate Django view to settings.LOGIN_URL. For example, using the defaults, add the following line to your URLconf:

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

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

  • If called via GET, it displays a login form that POSTs to the same URL. More on this in a bit.
  • If called via POST, it tries to log the user in. If login is successful, the view redirects to the URL specified in next. If next isn't provided, it redirects to settings.LOGIN_REDIRECT_URL (which defaults to /accounts/profile/). If login isn't successful, it redisplays the login form.

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

  • form: A FormWrapper object representing the login form. See the forms documentation? for more on FormWrapper objects.
  • next: The URL to redirect to after successful login. This may contain a query string, too.
  • site_name: The name of the current Site, according to the SITE_ID setting. If you're using the Django development version and you don't have the site framework installed, this will be set to the value of request.META['SERVER_NAME']. For more on sites, see the site framework docs?.

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

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

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

{% extends "base.html" %}

{% block content %}

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

<form method="post" action=".">
<table>
<tr><td><label for="id_username">Username:</label></td><td>{{ form.username }}</td></tr>
<tr><td><label for="id_password">Password:</label></td><td>{{ form.password }}</td></tr>
</table>

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

{% endblock %}

Other built-in views

In addition to the login view, the authentication system includes a few other useful built-in views:

django.contrib.auth.views.logout

Description:

Logs a user out.

Optional arguments:

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

Template context:

  • title: The string "Logged out", localized.

django.contrib.auth.views.logout_then_login

Description:

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

Optional arguments:

  • login_url: The URL of the login page to redirect to. This will default to settings.LOGIN_URL if not supplied.

django.contrib.auth.views.password_change

Description:

Allows a user to change their password.

Optional arguments:

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

Template context:

  • form: The password change form.

django.contrib.auth.views.password_change_done

Description:

The page shown after a user has changed their password.

Optional arguments:

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

django.contrib.auth.views.password_reset

Description:

Allows a user to reset their password, and sends them the new password in an email.

Optional arguments:

  • template_name: The full name of a template to use for displaying the password reset form. This will default to registration/password_reset_form.html if not supplied.
  • email_template_name: The full name of a template to use for generating the email with the new password. This will default to registration/password_reset_email.html if not supplied.

Template context:

  • form: The form for resetting the user's password.

django.contrib.auth.views.password_reset_done

Description:

The page shown after a user has reset their password.

Optional arguments:

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

django.contrib.auth.views.redirect_to_login

Description:

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

Required arguments:

  • next: The URL to redirect to after a successful login.

Optional arguments:

  • login_url: The URL of the login page to redirect to. This will default to settings.LOGIN_URL if not supplied.

Built-in manipulators

If you don't want to use the built-in views, but want the convenience of not having to write manipulators for this functionality, the authentication system provides several built-in manipulators:

  • django.contrib.auth.forms.AdminPasswordChangeForm: A manipulator used in the admin interface to change a user's password.
  • django.contrib.auth.forms.AuthenticationForm: A manipulator for logging a user in.
  • django.contrib.auth.forms.PasswordChangeForm: A manipulator for allowing a user to change their password.
  • django.contrib.auth.forms.PasswordResetForm: A manipulator for resetting a user's password and emailing the new password to them.
  • django.contrib.auth.forms.UserCreationForm: A manipulator for creating a new user.

Limiting access to logged-in users that pass a test

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

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

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

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

from django.contrib.auth.decorators import user_passes_test

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

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

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

from django.contrib.auth.decorators import user_passes_test

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

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

user_passes_test() takes an optional login_url argument, which lets you specify the URL for your login page (settings.LOGIN_URL by default).

Example in Python 2.3 syntax:

from django.contrib.auth.decorators import user_passes_test

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

Example in Python 2.4 syntax:

from django.contrib.auth.decorators import user_passes_test

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

The permission_required decorator

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

from django.contrib.auth.decorators import permission_required

def my_view(request):
    # ...
my_view = permission_required('polls.can_vote')(my_view)

Note that permission_required() also takes an optional login_url parameter. Example:

from django.contrib.auth.decorators import permission_required

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

As in the login_required decorator, login_url defaults to settings.LOGIN_URL.

Limiting access to generic views

To limit access to a generic view?, write a thin wrapper around the view, and point your URLconf to your wrapper instead of the generic view itself. For example:

from django.views.generic.date_based import object_detail

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

Permissions

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

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

The Django admin site uses permissions as follows:

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

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

Default permissions

Three basic permissions - add, change and delete - are automatically created for each Django model that has a class Admin set. Behind the scenes, these permissions are added to the auth_permission database table when you run manage.py syncdb.

Note that if your model doesn't have class Admin set when you run syncdb, the permissions won't be created. If you initialize your database and add class Admin to models after the fact, you'll need to run manage.py syncdb again. It will create any missing permissions for all of your installed apps.

Custom permissions

To create custom permissions for a given model object, use the permissions model Meta attribute?.

This example model creates three custom permissions:

class USCitizen(models.Model):
    # ...
    class Meta:
        permissions = (
            ("can_drive", "Can drive"),
            ("can_vote", "Can vote in elections"),
            ("can_drink", "Can drink alcohol"),
        )

The only thing this does is create those extra permissions when you run syncdb.

API reference

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

Fields

Permission objects have the following fields:

  • name - Required. 50 characters or fewer. Example: 'Can vote'.
  • content_type - Required. A reference to the django_content_type database table, which contains a record for each installed Django model.
  • codename - Required. 100 characters or fewer. Example: 'can_vote'.

Methods

Permission objects have the standard data-access methods like any other Django model?.

Authentication data in templates

The currently logged-in user and his/her permissions are made available in the template context? when you use RequestContext.

Technicality

Technically, these variables are only made available in the template context if you use RequestContext *and* your TEMPLATE_CONTEXT_PROCESSORS setting contains "django.core.context_processors.auth", which is default. For more, see the RequestContext docs?.

Users

The currently logged-in user, either a User instance or anAnonymousUser instance, is stored in the template variable {{ user }} :

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

Permissions

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

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

{{ perms.foo }}

Two-level-attribute lookup is a proxy to User.has_perm. This example would display True if the logged-in user had the permission foo.can_vote:

{{ perms.foo.can_vote }}

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

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

Groups

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

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

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

Messages

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

A message is associated with a User. There's no concept of expiration or timestamps.

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

The API is simple:

  • To create a new message, use user_obj.message_set.create(message='message_text').
  • To retrieve/delete messages, use user_obj.get_and_delete_messages(), which returns a list of Message objects in the user's queue (if any) and deletes the messages from the queue.

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

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

When you use RequestContext, the currently logged-in user and his/her messages are made available in the template context? as the template variable {{ messages }} . Here's an example of template code that displays messages:

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

Note that RequestContext calls get_and_delete_messages behind the scenes, so any messages will be deleted even if you don't display them.

Finally, note that this messages framework only works with users in the user database. To send messages to anonymous users, use the session framework?.

Other authentication sources

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

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

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

Specifying authentication backends

Behind the scenes, Django maintains a list of "authentication backends" that it checks for authentication. When somebody calls django.contrib.auth.authenticate() - as described 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 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, AUTHENTICATION_BACKENDS is set to:

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

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

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

Writing an authentication backend

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

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

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

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

But it could also authenticate a token, like so:

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

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

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

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

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

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

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

    ADMIN_LOGIN = 'admin'
    ADMIN_PASSWORD = 'sha1$4e987$afbcf42e21bd417fb71db8c66b321e9fc33051de'
    """
    def authenticate(self, username=None, password=None):
        login_valid = (settings.ADMIN_LOGIN == username)
        pwd_valid = check_password(password, settings.ADMIN_PASSWORD)
        if login_valid and pwd_valid:
            try:
                user = User.objects.get(username=username)
            except User.DoesNotExist:
                # Create a new user. Note that we can set password
                # to anything, because it won't be checked; the password
                # from settings.py will.
                user = User(username=username, password='get from settings.py')
                user.is_staff = True
                user.is_superuser = True
                user.save()
            return user
        return None

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

Handling authorization in custom backends

Custom auth backends can provide their own permissions.

The user model will delegate permission lookup functions (get_group_permissions(), get_all_permissions(), has_perm(), and has_module_perms()) to any authentication backend that implements these functions.

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

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

class SettingsBackend:

    # ...

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

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

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