+
−import datetime
+
−from django.core.exceptions import ImproperlyConfigured
+
−
+
−SESSION_KEY = '_auth_user_id'
+
−BACKEND_SESSION_KEY = '_auth_user_backend'
+
−REDIRECT_FIELD_NAME = 'next'
+
−
+
−def load_backend(path):
+
−    i = path.rfind('.')
+
−    module, attr = path[:i], path[i+1:]
+
−    try:
+
−        mod = __import__(module, {}, {}, [attr])
+
−    except ImportError, e:
+
−        raise ImproperlyConfigured, 'Error importing authentication backend %s: "%s"' % (module, e)
+
−    except ValueError, e:
+
−        raise ImproperlyConfigured, 'Error importing authentication backends. Is AUTHENTICATION_BACKENDS a correctly defined list or tuple?'
+
−    try:
+
−        cls = getattr(mod, attr)
+
−    except AttributeError:
+
−        raise ImproperlyConfigured, 'Module "%s" does not define a "%s" authentication backend' % (module, attr)
+
−    return cls()
+
−
+
−def get_backends():
+
−    from django.conf import settings
+
−    backends = []
+
−    for backend_path in settings.AUTHENTICATION_BACKENDS:
+
−        backends.append(load_backend(backend_path))
+
−    return backends
+
−
+
−def authenticate(**credentials):
+
−    """
+
−    If the given credentials are valid, return a User object.
+
−    """
+
−    for backend in get_backends():
+
−        try:
+
−            user = backend.authenticate(**credentials)
+
−        except TypeError:
+
−            # This backend doesn't accept these credentials as arguments. Try the next one.
+
−            continue
+
−        if user is None:
+
−            continue
+
−        # Annotate the user object with the path of the backend.
+
−        user.backend = "%s.%s" % (backend.__module__, backend.__class__.__name__)
+
−        return user
+
−
+
−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.
+
−    """
+
−    if user is None:
+
−        user = request.user
+
−    # TODO: It would be nice to support different login methods, like signed cookies.
+
−    user.last_login = datetime.datetime.now()
+
−    user.save()
+
−
+
−    if SESSION_KEY in request.session:
+
−        if request.session[SESSION_KEY] != user.id:
+
−            # 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()
+
−    request.session[SESSION_KEY] = user.id
+
−    request.session[BACKEND_SESSION_KEY] = user.backend
+
−    if hasattr(request, 'user'):
+
−        request.user = user
+
−
+
−def logout(request):
+
−    """
+
−    Removes the authenticated user's ID from the request and flushes their
+
−    session data.
+
−    """
+
−    request.session.flush()
+
−    if hasattr(request, 'user'):
+
−        from django.contrib.auth.models import AnonymousUser
+
−        request.user = AnonymousUser()
+
−
+
−def get_user(request):
+
−    from django.contrib.auth.models import AnonymousUser
+
−    try:
+
−        user_id = request.session[SESSION_KEY]
+
−        backend_path = request.session[BACKEND_SESSION_KEY]
+
−        backend = load_backend(backend_path)
+
−        user = backend.get_user(user_id) or AnonymousUser()
+
−    except KeyError:
+
−        user = AnonymousUser()
+
−    return user