Malformed POST request cause TypeError in AdminSite.login()

[Vladimir Dmitriev]

I found that any visitor can cause a TypeError on Django site with enabled contrib.admin application. This can be done by sending malformed authentication POST request without username parameter but with LOGIN_FORM_KEY. This will cause following exception in AdminSite.login() function:

Traceback (most recent call last):

 File "/usr/local/lib/python2.5/site-packages/django/core/handlers/base.py", line 86, in get_response
   response = callback(request, *callback_args, **callback_kwargs)

 File "/usr/local/lib/python2.5/site-packages/django/contrib/admin/sites.py", line 141, in root
   return self.login(request)

 File "/usr/local/lib/python2.5/site-packages/django/views/decorators/cache.py", line 44, in _wrapped_view_func
   response = view_func(request, *args, **kwargs)

 File "/usr/local/lib/python2.5/site-packages/django/contrib/admin/sites.py", line 244, in login
   if u'@' in username:

TypeError: argument of type 'NoneType' is not iterable

Although there is no security threat with this error, it makes Django incompatible with McAfee SECURE service. McAfee performs a sort of stress testing by generating a lot of random requests with different URLs and form parameters which cause ~20 Django error messages to appear in mailbox each day.

I've created tiny patch with fix and test.

[Ramiro Morales]

deuplicate of #11061