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.
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 custom permissions that can be checked through Django’s authorization system.
You can extend the default User model, or substitute a completely customized model.
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 authentication backend reference <authentication-backends-reference> for information on the authentication backends included with Django.
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 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 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 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().
If a backend raises a PermissionDenied exception, authentication will immediately fail. Django won’t check the backends that follow.
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 authorization methods.
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(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
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(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 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.
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 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.
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.
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.
To create custom permissions for a given model object, use the permissions model Meta attribute.
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 manage.py 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')
There are two ways to extend the default 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 proxy model based on 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 one-to-one relationship 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 InlineModelAdmin (for this example, we’ll use a StackedInline) in your app’s admin.py and add it to a UserAdmin class which is registered with the 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 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.
Prior to 1.5, a single profile model could be spedified site-wide with the setting AUTH_PROFILE_MODULE with a string consisting of the following items, separated by a dot:
For example, if the profile model was a class named UserProfile and was defined inside an application named accounts, the appropriate setting would be:
AUTH_PROFILE_MODULE = 'accounts.UserProfile'
When a user profile model has been defined and specified in this manner, each User object will have a method – get_profile() – which returns the instance of the user profile model associated with that User.
The method get_profile() does not create a profile if one does not exist.
Some kinds of projects may have authentication requirements for which Django’s built-in 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 AUTH_USER_MODEL setting that references a custom model:
AUTH_USER_MODEL = 'myapp.MyUser'
This dotted pair describes the name of the Django app, and the name of the Django model that you wish to use as your User model.
Warning
Changing 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 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.
If you reference User directly (for example, by referring to it in a foreign key), your code will not work in projects where the AUTH_USER_MODEL setting has been changed to a different User model.
Instead of referring to 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 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 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)
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.
The easiest way to construct a compliant custom User model is to inherit from AbstractBaseUser. AbstractBaseUser provides the core implementation of a User model, including hashed passwords and tokenized password resets. You must then provide some key implementation details:
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. 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'
A list of the field names that must be provided when creating a user. 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.
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 attribute on the builtin user model for details.
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.
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 django.contrib.auth.User.get_full_name().
The following methods are available on any subclass of AbstractBaseUser:
Returns the value of the field nominated by USERNAME_FIELD.
Always returns False. This is a way of differentiating from AnonymousUser objects. Generally, you should prefer using is_authenticated() to this method.
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.
Sets the user’s password to the given raw string, taking care of the password hashing. Doesn’t save the AbstractBaseUser object.
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.)
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 AbstractBaseUser object.
You may need this if authentication for your application takes place against an existing external source such as an LDAP directory.
Returns False if 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 UserManager; however, if your User model defines different fields, you will need to define a custom manager that extends BaseUserManager providing two additional methods:
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
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.
BaseUserManager provides the following utility methods:
A classmethod that normalizes email addresses by lowercasing the domain portion of the email address.
Retrieves a user instance using the contents of the field nominated by USERNAME_FIELD.
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:
If you’re entirely happy with Django’s User model and you just want to add some additional profile information, you can simply subclass AbstractUser and add your custom profile fields.
As you may expect, built-in Django’s forms and 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.
Depends on the User model. Must be re-written for any custom user model.
Depends on the User model. Must be re-written for any custom user model.
Works with any subclass of AbstractBaseUser, and will adapt to use the field defined in USERNAME_FIELD.
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.
Works with any subclass of AbstractBaseUser
Works with any subclass of AbstractBaseUser
Works with any subclass of AbstractBaseUser
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:
Returns True if the user is allowed to have access to the admin site.
Returns True if the user account is currently active.
Returns True if the user has the named permission. If obj is provided, the permission needs to be checked against a specific object instance.
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 AbstractUser, you can use Django’s existing UserAdmin class. However, if your User model extends AbstractBaseUser, you’ll need to define a custom ModelAdmin class. It may be possible to subclass the default UserAdmin; however, you’ll need to override any of the definitions that refer to fields on AbstractUser that aren’t on your custom User class.
To make it easy to include Django’s permission framework into your own User class, Django provides 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.
PermissionsMixin provides the following methods and attributes:
Boolean. Designates that this user has all permissions without explicitly assigning them.
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.
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.
Returns True if the user has the specified permission, where perm is in the format "<app label>.<permission codename>" (see permissions). 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.
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.
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.
ModelBackend
If you don’t include the 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.
One limitation of custom User models is that installing a custom User model will break any proxy model extending 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.
Another limitation of custom User models is that you can’t use 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 Signals for more information on registering an sending signals.
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:
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()
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 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=MyUserManager.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
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
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',)}),
('Important dates', {'fields': ('last_login',)}),
)
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)
Dec 23, 2012