Empty settings.AUTHENTICATION_BACKENDS creates hard to trace problem

[joel3000]

This is an obscure problem. If in settings.py the AUTHENTICATION_BACKENDS list is empty (i.e. AUTHENTICATION_BACKENDS=()),
then there will be no backends available to authenticate as it will override the django default behavior of using the default auth code.

When this occurs the auth login screen will just return a generic error about invalid username and password that is a pain to trace.

Unfortunately, I don't have time to figure out how to submit this change by the procedure but here is what I suggest to fix it.

In django/contrib/auth/init.py , add this check to get_backends():

def get_backends():
    from django.conf import settings
    backends = []
    for backend_path in settings.AUTHENTICATION_BACKENDS:
        backends.append(load_backend(backend_path))
 #### new code start####    
  if len(backends)==0:
        raise ImproperlyConfigured, 'settings.AUTHENTICATION_BACKENDS is empty.'
   #### new code end ##### 
return backends

It's an obscure problem, but it does seem to violate the "no magic" rule for django, and it tripped me up for a day
having to hunt it down.

[James Bennett]

This is enough of an edge case (you have to manually clear AUTHENTICATION_BACKENDS to trigger it) that it's not 1.2-critical.

[Gabriel Hurley]

Test added. I'll agree with James Bennett about it not being critical for 1.2. I've certainly never run into this bug myself. It seems like a pretty safe/stable change though... Either way, I've got no stake in it personally.

[Gabriel Hurley]

Bumping to 1.3 milestone.

[Gabriel Hurley]

Added an updated patch which applies cleanly to trunk.

[Paul McMillan]

This patch looks good to me. Marking as RFC.

[Alex Gaynor]

The code really should be changed to use the raise Exception("message") syntax.

[Łukasz Rekucki]

Use new exception syntax.

[Russell Keith-Magee]

(In [14793]) Fixed #13190 -- Improved error handling for the case where no authentication backends are defined. Thanks to Joel3000 for the report, and Łukasz Rekucki for the final patch.

[Russell Keith-Magee]

(In [14799]) [1.2.X] Fixed #13190 -- Improved error handling for the case where no authentication backends are defined. Thanks to Joel3000 for the report, and Łukasz Rekucki for the final patch.

Backport of r14793 from trunk.

[Jacob]

Milestone 1.3 deleted