Permission-checking views

The ObjectPermissionRequiredMixin view combines Django’s PermissionRequiredMixin and SingleObjectMixin views, and performs the permission check against the object that was looked up.

Use it like the base classes:

from auth_utils.views import ObjectPermissionRequiredMixin


class ArticleDetail(ObjectPermissionRequiredMixin, generic.DetailView):
    model = Article
    permission_required = ['news.read_article']


class ArticleUpdate(ObjectPermissionRequiredMixin, generic.UpdateView):
    model = Article
    permission_required = ['news.change_article']

Permission-checking in templates

Load the template tag library:

{% load auth_utils %}

The perms filter allows checking object-level permissions with a convenient syntax:

{% if perm in user|perms:object %} ... {% endif %}

The object argument is optional. If omitted, the global permission is checked, similar to Django’s perms object.

Examples:

{% if 'news.read_article' in user|perms:article %}
    {{ article.text }}
{% else %}
    You do not have permission to read this article.
{% endif %}


{% if 'news.change_article' in user|perms:article %}
    <a href="...">Edit article</a>
{% endif %}

{% if 'news.delete_article' in user|perms:article %}
    <a href="...">Delete article</a>
{% endif %}

The library provides can_change and can_delete shorthands for checking Django’s default app.change_model and app.delete_model model permissions:

{% if user|can_change:article %} <a href="...">Edit</a> {% endif %}
{% if user|can_delete:article %} <a href="...">Delete</a> {% endif %}

BaseAuthorizationBackend

This base class provides all the boilerplate code necessary for a Django authentication backend to work, without performing any user authentication or permission authorization itself.

This is intended to make it easy to write custom authorization policies that only implement the backend methods they’re interested in:

from auth_utils.backends import BaseAuthorizationBackend


class ArticleEditPolicy(BaseAuthorizationBackend):
    """
    Allow authors to change and delete their own articles.
    """

    def get_user_permissions(self, user_obj, obj=None):
        is_author = isinstance(obj, Article) and article.author == user_obj
        if user_obj.is_active and is_author:
            return {'news.change_article', 'news.delete_article'}
        else:
            return set()


class GuestAccessPolicy(BaseAuthorizationBackend):
    """
    Allow anonymous users to read non-premium articles.
    """

    def get_user_permissions(self, user_obj, obj=None):
        guest_readable = isinstance(obj, Article) and not article.is_premium
        if not user_obj.is_authenticated() and guest_readable:
            return {'news.read_article'}
        else:
            return set()

Once defined, these policies can be enabled in AUTHENTICATION_BACKENDS:

AUTHENTICATION_BACKENDS = [
    'django.contrib.auth.backends.ModelBackend',

    # Custom authorization policies
    'news.auth.ArticleEditPolicy',
    'news.auth.GuestAccessPolicy',
]