[1.9.x] Refs #25878 -- Added the expected return type of CSRF_FAILURE_VIEW.

Default: ``'django.views.csrf.csrf_failure'``

A dotted path to the view function to be used when an incoming request

is rejected by the CSRF protection.  The function should have this signature::

A dotted path to the view function to be used when an incoming request is

rejected by the :doc:`CSRF protection </ref/csrf>`. The function should have

this signature::

    def csrf_failure(request, reason=""):

        ...

where ``reason`` is a short message (intended for developers or logging, not for

end users) indicating the reason the request was rejected.  See

:doc:`/ref/csrf`.

where ``reason`` is a short message (intended for developers or logging, not

for end users) indicating the reason the request was rejected. It should return

an :class:`~django.http.HttpResponseForbidden`.

.. setting:: CSRF_HEADER_NAME