# Django 1.8.18.dev20170123152445 documentation

# Source code for django.contrib.auth.backends

    from __future__ import unicode_literals

    from django.contrib.auth import get_user_model
    from django.contrib.auth.models import Permission

    class ModelBackend(object):
        """
        Authenticates against settings.AUTH_USER_MODEL.
        """

        def authenticate(self, username=None, password=None, **kwargs):
            UserModel = get_user_model()
            if username is None:
                username = kwargs.get(UserModel.USERNAME_FIELD)
            try:
                user = UserModel._default_manager.get_by_natural_key(username)
                if user.check_password(password):
                    return user
            except UserModel.DoesNotExist:
                # Run the default password hasher once to reduce the timing
                # difference between an existing and a non-existing user (#20760).
                UserModel().set_password(password)

        def _get_user_permissions(self, user_obj):
            return user_obj.user_permissions.all()

        def _get_group_permissions(self, user_obj):
            user_groups_field = get_user_model()._meta.get_field('groups')
            user_groups_query = 'group__%s' % user_groups_field.related_query_name()
            return Permission.objects.filter(**{user_groups_query: user_obj})

        def _get_permissions(self, user_obj, obj, from_name):
            """
            Returns the permissions of `user_obj` from `from_name`. `from_name` can
            be either "group" or "user" to return permissions from
            `_get_group_permissions` or `_get_user_permissions` respectively.
            """
            if not user_obj.is_active or user_obj.is_anonymous() or obj is not None:
                return set()

            perm_cache_name = '_%s_perm_cache' % from_name
            if not hasattr(user_obj, perm_cache_name):
                if user_obj.is_superuser:
                    perms = Permission.objects.all()
                else:
                    perms = getattr(self, '_get_%s_permissions' % from_name)(user_obj)
                perms = perms.values_list('content_type__app_label', 'codename').order_by()
                setattr(user_obj, perm_cache_name, set("%s.%s" % (ct, name) for ct, name in perms))
            return getattr(user_obj, perm_cache_name)

        def get_user_permissions(self, user_obj, obj=None):
            """
            Returns a set of permission strings the user `user_obj` has from their
            `user_permissions`.
            """
            return self._get_permissions(user_obj, obj, 'user')

        def get_group_permissions(self, user_obj, obj=None):
            """
            Returns a set of permission strings the user `user_obj` has from the
            groups they belong.
            """
            return self._get_permissions(user_obj, obj, 'group')

        def get_all_permissions(self, user_obj, obj=None):
            if not user_obj.is_active or user_obj.is_anonymous() or obj is not None:
                return set()
            if not hasattr(user_obj, '_perm_cache'):
                user_obj._perm_cache = self.get_user_permissions(user_obj)
                user_obj._perm_cache.update(self.get_group_permissions(user_obj))
            return user_obj._perm_cache

        def has_perm(self, user_obj, perm, obj=None):
            if not user_obj.is_active:
                return False
            return perm in self.get_all_permissions(user_obj, obj)

        def has_module_perms(self, user_obj, app_label):
            """
            Returns True if user_obj has any permissions in the given app_label.
            """
            if not user_obj.is_active:
                return False
            for perm in self.get_all_permissions(user_obj):
                if perm[:perm.index('.')] == app_label:
                    return True
            return False

        def get_user(self, user_id):
            UserModel = get_user_model()
            try:
                return UserModel._default_manager.get(pk=user_id)
            except UserModel.DoesNotExist:
                return None

    class RemoteUserBackend(ModelBackend):
        """
        This backend is to be used in conjunction with the ``RemoteUserMiddleware``
        found in the middleware module of this package, and is used when the server
        is handling authentication outside of Django.

        By default, the ``authenticate`` method creates ``User`` objects for
        usernames that don't already exist in the database.  Subclasses can disable
        this behavior by setting the ``create_unknown_user`` attribute to
        ``False``.
        """

        # Create a User object if not already in the database?
        create_unknown_user = True

        def authenticate(self, remote_user):
            """
            The username passed as ``remote_user`` is considered trusted.  This
            method simply returns the ``User`` object with the given username,
            creating a new ``User`` object if ``create_unknown_user`` is ``True``.

            Returns None if ``create_unknown_user`` is ``False`` and a ``User``
            object with the given username is not found in the database.
            """
            if not remote_user:
                return
            user = None
            username = self.clean_username(remote_user)

            UserModel = get_user_model()

            # Note that this could be accomplished in one try-except clause, but
            # instead we use get_or_create when creating unknown users since it has
            # built-in safeguards for multiple threads.
            if self.create_unknown_user:
                user, created = UserModel._default_manager.get_or_create(**{
                    UserModel.USERNAME_FIELD: username
                })
                if created:
                    user = self.configure_user(user)
            else:
                try:
                    user = UserModel._default_manager.get_by_natural_key(username)
                except UserModel.DoesNotExist:
                    pass
            return user

        def clean_username(self, username):
            """
            Performs any cleaning on the "username" prior to using it to get or
            create the user object.  Returns the cleaned username.

            By default, returns the username unchanged.
            """
            return username

        def configure_user(self, user):
            """
            Configures a user after creation and returns the updated user.

            By default, returns the user unmodified.
            """
            return user