=========================================
How to authenticate using ``REMOTE_USER``
=========================================

This document describes how to make use of external authentication sources
(where the web server sets the ``REMOTE_USER`` environment variable) in your
Django applications. This type of authentication solution is typically seen on
intranet sites, with single sign-on solutions such as IIS and Integrated
Windows Authentication or Apache and `mod_authnz_ldap`_, `CAS`_, `WebAuth`_,
`mod_auth_sspi`_, etc.

.. _mod_authnz_ldap: https://httpd.apache.org/docs/current/mod/mod_authnz_ldap.html
.. _CAS: https://www.apereo.org/projects/cas
.. _WebAuth: https://uit.stanford.edu/service/authentication
.. _mod_auth_sspi: https://sourceforge.net/projects/mod-auth-sspi

When the web server takes care of authentication it typically sets the
``REMOTE_USER`` environment variable for use in the underlying application. In
Django, ``REMOTE_USER`` is made available in the :attr:`request.META
<django.http.HttpRequest.META>` attribute. Django can be configured to make
use of the ``REMOTE_USER`` value using the ``RemoteUserMiddleware``
or ``PersistentRemoteUserMiddleware``, and
:class:`~django.contrib.auth.backends.RemoteUserBackend` classes found in
:mod:`django.contrib.auth`.

Configuration
=============

First, you must add the
:class:`django.contrib.auth.middleware.RemoteUserMiddleware` to the
:setting:`MIDDLEWARE` setting **after** the
:class:`django.contrib.auth.middleware.AuthenticationMiddleware`::

    MIDDLEWARE = [
        "...",
        "django.contrib.auth.middleware.AuthenticationMiddleware",
        "django.contrib.auth.middleware.RemoteUserMiddleware",
        "...",
    ]

Next, you must replace the :class:`~django.contrib.auth.backends.ModelBackend`
with :class:`~django.contrib.auth.backends.RemoteUserBackend` in the
:setting:`AUTHENTICATION_BACKENDS` setting::

    AUTHENTICATION_BACKENDS = [
        "django.contrib.auth.backends.RemoteUserBackend",
    ]

With this setup, ``RemoteUserMiddleware`` will detect the username in
``request.META['REMOTE_USER']`` and will authenticate and auto-login that user
using the :class:`~django.contrib.auth.backends.RemoteUserBackend`.

Be aware that this particular setup disables authentication with the default
``ModelBackend``. This means that if the ``REMOTE_USER`` value is not set
then the user is unable to log in, even using Django's admin interface.
Adding ``'django.contrib.auth.backends.ModelBackend'`` to the
``AUTHENTICATION_BACKENDS`` list will use ``ModelBackend`` as a fallback
if ``REMOTE_USER`` is absent, which will solve these issues.

Django's user management, such as the views in ``contrib.admin`` and
the :djadmin:`createsuperuser` management command, doesn't integrate with
remote users. These interfaces work with users stored in the database
regardless of ``AUTHENTICATION_BACKENDS``.

.. note::

    Since the ``RemoteUserBackend`` inherits from ``ModelBackend``, you will
    still have all of the same permissions checking that is implemented in
    ``ModelBackend``.

    Users with :attr:`is_active=False
    <django.contrib.auth.models.User.is_active>` won't be allowed to
    authenticate. Use
    :class:`~django.contrib.auth.backends.AllowAllUsersRemoteUserBackend` if
    you want to allow them to.

If your authentication mechanism uses a custom HTTP header and not
``REMOTE_USER``, you can subclass ``RemoteUserMiddleware`` and set the
``header`` attribute to the desired ``request.META`` key. For example:

.. code-block:: python
   :caption: ``mysite/middleware.py``

    from django.contrib.auth.middleware import RemoteUserMiddleware


    class CustomHeaderRemoteUserMiddleware(RemoteUserMiddleware):
        header = "HTTP_AUTHUSER"

This custom middleware is then used in the :setting:`MIDDLEWARE` setting
instead of :class:`django.contrib.auth.middleware.RemoteUserMiddleware`::

    MIDDLEWARE = [
        "...",
        "django.contrib.auth.middleware.AuthenticationMiddleware",
        "mysite.middleware.CustomHeaderRemoteUserMiddleware",
        "...",
    ]

.. warning::

    ``RemoteUserMiddleware`` must not be deployed in configurations where a
    client can supply the header. You must be sure that your web server or
    reverse proxy always sets or strips that header based on the appropriate
    authentication checks, never permitting an end user to submit a fake (or
    "spoofed") header value. In particular, ASGI deployments cannot be exposed
    directly to the internet (that is, without a reverse proxy) when using this
    middleware.

    Since the HTTP headers ``X-Auth-User`` and ``X-Auth_User`` (for example)
    both normalize to the ``HTTP_X_AUTH_USER`` key in ``request.META``, you
    must also check that your web server doesn't allow a spoofed header using
    underscores in place of dashes.

    Under WSGI, this warning doesn't apply to ``RemoteUserMiddleware`` in its
    default configuration with ``header = "REMOTE_USER"``, since a key that
    doesn't start with ``HTTP_`` in ``request.META`` can only be set by your
    WSGI server, not directly from an HTTP request header. This warning *does*
    apply by default on ASGI, because in the async path, the middleware
    prepends ``HTTP_`` to the defined header name before looking it up in
    ``request.META``.

If you need more control, you can create your own authentication backend
that inherits from :class:`~django.contrib.auth.backends.RemoteUserBackend` and
override one or more of its attributes and methods.

.. _persistent-remote-user-middleware-howto:

Using ``REMOTE_USER`` on login pages only
=========================================

The ``RemoteUserMiddleware`` authentication middleware assumes that the HTTP
request header ``REMOTE_USER`` is present with all authenticated requests. That
might be expected and practical when Basic HTTP Auth with ``htpasswd`` or
similar mechanisms are used, but with Negotiate (GSSAPI/Kerberos) or other
resource intensive authentication methods, the authentication in the front-end
HTTP server is usually only set up for one or a few login URLs, and after
successful authentication, the application is supposed to maintain the
authenticated session itself.

:class:`~django.contrib.auth.middleware.PersistentRemoteUserMiddleware`
provides support for this use case. It will maintain the authenticated session
until explicit logout by the user. The class can be used as a drop-in
replacement of :class:`~django.contrib.auth.middleware.RemoteUserMiddleware`
in the documentation above.
