[PYTHON] How to update user information when logging in to Django RemoteUserMiddleware

background

Use RemoteUserMiddleware to do SSO with Django.

On the Django app side, the environment variable REMOTE_USER set by the SAML module (Shibboleth in the own environment) is used as ID information to identify the user, but at this time, attributes other than the ID information (for example, email) are also included in the User class on the Django app side. I want to capture it.

Related article: Django + Shibboleth with RemoteUserMiddleware (Explanation of introduction of RemoteUserMiddleware)

environment

--Windows Server 2016 (not directly related) --Apache 2.4 (not directly related) --Python 3.7.7 (not directly related)

• Django 3.0 --Shibboleth Service Provider 3.x (not directly related)

Prerequisite knowledge

RemoteUserBackend searches for an object whose username has the environment variable REMOTE_USER from the User model specified by settings.AUTH_USER_MODEL. If found, log in as that user. If not found, create a User object with REMOTE_USER as username and log in (this setting can be changed).

Step 1: Override configure_user

Originally, RemoteUserBackend uses the method for manipulating the User object when creating the User object on the Django application side.

python:django.contrib.auth.backends

class RemoteUserBackend(ModelBackend):
...
    def configure_user(self, request, user):
        """
        Configure a user after creation and return the updated user.

        By default, return the user unmodified.
        """
        return user

Create backends.py (any name) in a suitable app.

appname
└── appname
    ├── templates
    ├── __init__.py
    ├── settings.py
    ├── urls.py
    ├── views.py
    ├── wsgi.py
    └── backends.py  #← Create

Override configure_user. This time, I decided to input the attribute ʻATR_mail` added by Shibboleth to the HTTP Header in the User object.

backends.py

from django.contrib.auth.backends import RemoteUserBackend

class MyRemoteUserBackend(RemoteUserBackend):
    def configure_user(self, request, user: MyUser):
        user.email = request.META['ATR_mail']
        user.save() #← Don't forget! !!
        return user

To enable this, you need to change ʻAUTHENTICATION_BACKENDS in settings.py`.

settings.py

AUTHENTICATION_BACKENDS = (
    # 'django.contrib.auth.backends.RemoteUserBackend', #← Delete
    'appname.backends.MyRemoteUserBackend', #← Add
    'django.contrib.auth.backends.ModelBackend',
)

Step 2: Override ʻauthenticate`

Overriding configure_user will only execute configure_user if you create a new User object for Django's first-time REMOTE_USER and log in. ** **

Even if the attribute information on the IdP side changes, the existing User object is not updated, but this seems to be inconvenient in many cases. For example, if you are using SSO in a company and the department or extension number changes from time to time.

In that case, you have to modify ʻauthenticate. Fortunately, you can use the MyRemoteUserBackend of backends.pycreated earlier. Most are copies of the superclassRemoteUserBackend ʻauthenticate.

backends.py

from django.contrib.auth.backends import RemoteUserBackend

from django.contrib.auth.models import User

import inspect
import warnings

from django.contrib.auth import get_user_model
from django.utils.deprecation import RemovedInDjango31Warning

UserModel = get_user_model()

class MyRemoteUserBackend(RemoteUserBackend):

    def authenticate(self, request, remote_user):
        """
        The username passed as ``remote_user`` is considered trusted. Return
        the ``User`` object with the given username. Create a new ``User``
        object if ``create_unknown_user`` is ``True``.

        Return None if ``create_unknown_user`` is ``False`` and a ``User``
        object with the given username is not found in the database.
        """
        if not remote_user:
            return
        user = None
        username = self.clean_username(remote_user)

        # Note that this could be accomplished in one try-except clause, but
        # instead we use get_or_create when creating unknown users since it has
        # built-in safeguards for multiple threads.
        if self.create_unknown_user:
            user, created = UserModel._default_manager.get_or_create(**{
                UserModel.USERNAME_FIELD: username
            })
            if created:                                      #← Attention
                args = (request, user)
                try:
                    inspect.getcallargs(self.configure_user, request, user)
                except TypeError:
                    args = (user,)
                    warnings.warn(
                        'Update %s.configure_user() to accept `request` as '
                        'the first argument.'
                        % self.__class__.__name__, RemovedInDjango31Warning
                    )
                user = self.configure_user(*args)            #← Attention
            else:                                            #← Add
                user = self.configure_user(request, user)    #← Add
        else:
            try:
                user = UserModel._default_manager.get_by_natural_key(username)
            except UserModel.DoesNotExist:
                pass
        return user if self.user_can_authenticate(user) else None

    def configure_user(self, request, user: User):
        user.email = request.META['ATR_mail']
        user.save()
        return user

As stated in "Attention", configure_user is originally called only when created == True in ʻUserModel._default_manager.get_or_create`. This does not allow you to update existing user information.

Therefore, add two lines of "add" so that configure_user is called even when created! = True. If you want to separate the operation for creating a new User object and updating it, you can imitate configure_user and create a new ʻupdate_user` etc. so that it will be called.

that's all.