1.  Add django.contrib.auth to INSTALLED_APPS, if necessary.
2.  Add to urls.py:
    from django.contrib.auth.views import login, logout
    urlpatterns += patterns('',
        (r'^accounts/login/$', login),
        (r'^accounts/logout/$', logout),
    )
3.  Add templates/registration/login.html (note hidden field "next")
4.  Restrict private views to logged-in users:
    from django.contrib.auth.decorators import login_required
    @login_required
    def my_view(request):
        # ...
5.  Create a registration view and template