settings.py

AUTHENTICATION_BACKENDS = (
    'social_auth.backends.google.GoogleOAuth2Backend',
    'django.contrib.auth.backends.ModelBackend',
)
LOGIN_REDIRECT_URL = '/'

GOOGLE_OAUTH2_CLIENT_ID = os.environ['GOOGLE_OAUTH2_CLIENT_ID']
GOOGLE_OAUTH2_CLIENT_SECRET = os.environ['GOOGLE_OAUTH2_CLIENT_SECRET']
GOOGLE_WHITE_LISTED_DOMAINS = ['incuna.com']
SOCIAL_AUTH_USER_MODEL = 'auth.User'

urls.py

from django.conf.urls import *
from django.contrib import admin

from .views import AuthComplete, LoginError


admin.autodiscover()

urlpatterns = patterns('',
    # some other urls

    url(r'^admin/', include(admin.site.urls)),
    url(r'^complete/(?P<backend>[^/]+)/$', AuthComplete.as_view()),
    url(r'^login-error/$', LoginError.as_view()),
    url(r'', include('social_auth.urls')),
)

views.py

from django.core.urlresolvers import reverse
from django.contrib import messages
from django.http import HttpResponse, HttpResponseRedirect
from django.views.generic.base import View
from social_auth.backends.exceptions import AuthFailed
from social_auth.views import complete



class AuthComplete(View):
    def get(self, request, *args, **kwargs):
        backend = kwargs.pop('backend')
        try:
            return complete(request, backend, *args, **kwargs)
        except AuthFailed:
            messages.error(request, "Your Google Apps domain isn't authorized for this app")
            return HttpResponseRedirect(reverse('login'))


class LoginError(View):
    def get(self, request, *args, **kwargs):
        return HttpResponse(status=401)