authentification doesn't work about django-mongoengine HOT 19 CLOSED

 request.session[SESSION_KEY] = user._meta.pk.value_to_string(user)

MIDDLEWARE_CLASSES = (
    ...
    #'django.contrib.auth.middleware.AuthenticationMiddleware',
    'myapp.auth.AuthenticationMiddleware'
)

from django_mongoengine.auth.backends import get_user
from django.utils.functional import SimpleLazyObject

from django.contrib.auth import SESSION_KEY, BACKEND_SESSION_KEY, HASH_SESSION_KEY
from django.contrib.auth.signals import user_logged_in
from django.middleware.csrf import rotate_token

#SESSION_KEY = '_auth_user_id'

class AuthenticationMiddleware(object):
    def process_request(self, request):
        assert hasattr(request, 'session'), (
            "The Django authentication middleware requires session middleware "
            "to be installed. Edit your MIDDLEWARE_CLASSES setting to insert "
            "'django.contrib.sessions.middleware.SessionMiddleware' before "
            "'django.contrib.auth.middleware.AuthenticationMiddleware'."
        )
        request.user = SimpleLazyObject(lambda: get_user(_get_user_session_key(request)))

from bson.objectid import ObjectId
def _get_user_session_key(request):
    # This value in the session is always serialized to a string, so we need
    # to convert it back to Python whenever we access it.
    if SESSION_KEY in request.session:
        return ObjectId(request.session[SESSION_KEY])

def login(request, user):
    """
    Persist a user id and a backend in the request. This way a user doesn't
    have to reauthenticate on every request. Note that data set during
    the anonymous session is retained when the user logs in.
    """
    session_auth_hash = ''
    if user is None:
        user = request.user
    if hasattr(user, 'get_session_auth_hash'):
        session_auth_hash = user.get_session_auth_hash()

    if SESSION_KEY in request.session:
        if _get_user_session_key(request) != user.pk or (
                session_auth_hash and
                request.session.get(HASH_SESSION_KEY) != session_auth_hash):
            # To avoid reusing another user's session, create a new, empty
            # session if the existing session corresponds to a different
            # authenticated user.
            request.session.flush()
    else:
        request.session.cycle_key()
    try:
        request.session[SESSION_KEY] = user._meta.pk.value_to_string(user)
    except AttributeError:
        request.session[SESSION_KEY] = str(user.pk)
    request.session[BACKEND_SESSION_KEY] = user.backend
    request.session[HASH_SESSION_KEY] = session_auth_hash
    if hasattr(request, 'user'):
        request.user = user
    rotate_token(request)
    user_logged_in.send(sender=user.__class__, request=request, user=user)

from myapp.auth import login as auth_login

@sensitive_post_parameters()
@csrf_protect
@never_cache
def login(request, template_name='registration/login.html',
          redirect_field_name=REDIRECT_FIELD_NAME,
          authentication_form=AuthenticationForm,
          current_app=None, extra_context=None):
    """
    Displays the login form and handles the login action.
    """
    redirect_to = request.POST.get(redirect_field_name,
                                   request.GET.get(redirect_field_name, ''))

    if request.method == "POST":
        form = authentication_form(request, data=request.POST)
        if form.is_valid():

            # Ensure the user-originating redirection url is safe.
            if not is_safe_url(url=redirect_to, host=request.get_host()):
                redirect_to = resolve_url(settings.LOGIN_REDIRECT_URL)

            # Okay, security check complete. Log the user in.
            auth_login(request, form.get_user())

            return HttpResponseRedirect(redirect_to)
    else:
        form = authentication_form(request)

    current_site = get_current_site(request)

    context = {
        'form': form,
        redirect_field_name: redirect_to,
        'site': current_site,
        'site_name': current_site.name,
    }
    if extra_context is not None:
        context.update(extra_context)

    if current_app is not None:
        request.current_app = current_app

    return TemplateResponse(request, template_name, context)

urlpatterns = patterns('',
    url(r'^login/$', 'myapp.views.login', {'template_name': 'my_custom_template.html', 'current_app': 'myappl', 'authentication_form': MyAuthenticationForm}, name='login'),
    ...
)

'MetaDict' object has no attribute 'pk'
Request Method: GET
Request URL:    http://192.168.3.3:8000/authenticate/?code=6d77e581ec52af4d2d2e
Django Version: 1.8.6
Exception Type: AttributeError
Exception Value:    
'MetaDict' object has no attribute 'pk'
Exception Location: /usr/local/lib/python2.7/dist-packages/django/contrib/auth/__init__.py in login, line 111
Python Executable:  /usr/bin/python
Python Version: 2.7.6
Python Path:    
['/home/vagrant/cub/cub',
 '/usr/lib/python2.7',
 '/usr/lib/python2.7/plat-x86_64-linux-gnu',
 '/usr/lib/python2.7/lib-tk',
 '/usr/lib/python2.7/lib-old',
 '/usr/lib/python2.7/lib-dynload',
 '/usr/local/lib/python2.7/dist-packages',
 '/usr/lib/python2.7/dist-packages']
Server time:    Thu, 26 Nov 2015 10:35:16 +0000
-----
views.py in login
                        login(request, user) ...
▶ Local vars
/usr/local/lib/python2.7/dist-packages/django/contrib/auth/__init__.py in login
                request.session[SESSION_KEY] = user._meta.pk.value_to_string(user) 

AUTH_USER_MODEL = 'mongo_auth.MongoUser'

AUTHENTICATION_BACKENDS = (
    'django_mongoengine.mongo_auth.backends.MongoEngineBackend',
)