http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
10.4.2 401 Unauthorized
The request requires user authentication. The response MUST include a WWW-Authenticate header field (section 14.47) containing a challenge applicable to the requested resource. The client MAY repeat the request with a suitable Authorization header field (section 14.8). If the request already included Authorization credentials, then the 401 response indicates that authorization has been refused for those credentials. If the 401 response contains the same challenge as the prior response, and the user agent has already attempted authentication at least once, then the user SHOULD be presented the entity that was given in the response, since that entity might include relevant diagnostic information. HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication" [43].
See contrib/auth/handlers/modpython.py:
def authenhandler(req, **kwargs):
...
return apache.HTTP_UNAUTHORIZED
Django should not be using this response without also returning a correct WWW-Authenticate header field. The only response that makes sense in this context is a 403 Forbidden response as the authentication mentioned in the HTTP RFC is specifically HTTP authentication and not through the use of cookies.