Abu Ashraf Masnun

(This post is a part of a tutorial series on Building REST APIs in Django)

In our last post about ViewSet, ModelViewSet and Router, we saw how easily we can create REST APIs with the awesome Django REST Framework. In this blog post, we would see how we can secure our endpoints with user authentication and permissions. Authentication will help us identify which user is currently logged in and permissions will decide which user(s) can access which resources.

Authentication

The idea of authentication is pretty simple. When a new incoming request comes, we have to check the request and see if we can identify any user credentials along with it. If you have read the Flask HTTP Auth tutorial or the one about JWT, you might remember how we were checking the authorization header to authenticate our users. We might also receive the user login data via a POST request (form submission) or the user may already be logged in and we can identify using the session data.

We can see that the authentication mechanism can largely vary. Django REST Framework is very flexible in accommodating them. We can give DRF a list of classes, DRF will run the authenticate method on those classes. As soon as a class successfully authenticates the user, the return values from the call is set to request.user and request.auth. If none of the classes manage to authenticate the user, then the user is set to django.contrib.auth.models.AnonymousUser .

We can set these classes using the DEFAULT_AUTHENTICATION_CLASSES settings under the DRF settings. Here’s an example:

In the example above we used BasicAuthentication and SessionAuthentication – two of the built in classes from Django REST Framework. We will look at how they work and we will also check how we can write our own class for our custom authentication.

(PS: Here we set the authentication policy globally, for all views / paths / resources – if we want, we can also use different authentication mechanism for each one, individually but that is usually not done in most cases).

Basic Authentication

In our example before, we mentioned the BasicAuthentication class. This class first checks the http authorization header (HTTP_AUTHORIZATION in request.META ). If the header contains appropriate string (something like Basic <Base64 Encoded Login>), it will decode the string, split the username, password and try to authenticate the user.

Basic Authentication is very simple, easy to setup and might be quite convenient for testing / debugging but I would highly discourage using this method on production.

Session Authentication

If you have used Django, you already know about session based authentication. In fact, Django itself handles the session based auth and sets the user as part of the request object (an instance of HttpRequest object. DRF just reads the user data from the request and checks for CSRF. That’s it.

Session Authentication works very well if your users are interacting with your API on the web, perhaps using ajax calls? In such cases, if the user is once logged in, his/her auth is stored in the session and we can depend on those data while making requests from our web app. However, this will not work well if the client doesn’t or can not accept cookies (apps on different domains, mobile or desktop apps, other micro services etc).

Token Authentication

If you understand JWT, this one will feel similar, except in this case, the token will be just a “token”, no JSON or no signing. The user logs in and gets a token. On subsequent requests, this token must be passed as part of the authorization header.

To use token based auth, we first need to add the rest_framework.authtoken app to the INSTALLED_APPS list in your settings.py file. And then run the migration to create the related tables.

We also need to add the TokenAuthentication class to our DRF auth class list:

Now let’s create a view to issue tokens to user.

The code here should be self explanatory. We take username and password. We then try to authenticate the user using Django’s default authentication (checking username and password against what’s stored in the database). If the authentication fails, we return error message along with http status code 401. If the authentication succeeds, we issue a token for the user and pass it in the response.

We need to add this view to our urlpatterns next:

Now let’s try it out:

So we’re getting the tokens successfully. Now to access a secured resource, we need to pass it as part of the authorization header. But how do we make a resource available only to a logged in user? Well, permissions come into play here.

Permissions

While authentication tells us which user is logged in (or not), it’s our responsibility to check if the current user (a valid logged in user or a guest, not logged in visitor) has access to the resource. Permissions can help us deal with that. Just like authentication, we can also set a class of permissions globally or on each resource individually. Let’s start with the IsAuthenticated permission first. Let’s add this to our SubscriberViewSet.

If we try to access subscribers without any authentication, we will get an error message now:

So let’s provide authentication using the token we got.

Now it works fine! There are many useful, already provided permission classes with Django REST Framework. You can find a list of them here http://www.django-rest-framework.org/api-guide/permissions/#api-reference.

Custom Authentication and Permissions

The authentication and permission classes which come with DRF are quite enough for many cases. But what if we needed to create our own? Let’s see how we can do that.

Writing a custom authentication class is very simple. You define your custom authenticate method which would receive the request object. You will have to return an instance of the default User model if authentication succeeds, otherwise raise an exception. You can also return an optional value for the auth object to be set on request. If our authentication method can not be used for this request, we should return None so other classes are tried.

Here’s an example from DRF docs:

In this example, the username is being retrieved from a custom header (X_USERNAME) and the rest is quite easy to understand.

Next, let’s see how we can create our custom permission class. For permissions, we can have two types of permissions – global permission or per object permission. Here’s an example of global permission from DRF docs:

If the has_permission method returns True then the user has permission, otherwise not. Let’s see the example for per object permission:

For dealing with per object permission, we can override the has_object_permission method. It can take the request, the view and the obj. We have to check if the current user can access the obj in question. Just like before, we need to return True or False to allow or deny the request.

In this blog post, we learned the basics of authentication and permissions. We now know how we can secure our API endpoints with DRF. While the token based authentication was very useful, we kind of like JWT. So in our next post, we will be using a third party package to implement JWT for Django REST Framework.

(This post is a part of a tutorial series on Building REST APIs in Django)

In our last blog post on ModelSerializer and Generic Views, we demonstrated how we can use the generic views along with ModelSerializer classes to rapidly develop our REST APIs. In this post, we will discuss about ViewSet and ModelViewset and see how they can speed up building APIs even further. At the same time we will take a look at the concepts of Routers which allow us to manage our api routes in a cleaner fashion.

Understanding ViewSet

So far we have learned how we can use the generic views. We can now use them to create the two kinds of resources – “collections” and “elements”. It works very well but we need to write at least two different classes to handle them properly. But if we think about it, both resources focus on the same entity, the same model – “Subscriber”. Wouldn’t it make more sense if we could have all the actions related to a Subscriber in a single class? Wouldn’t that be more convenient if we can put all the Subscriber related logic in a single place?

ViewSets come to the rescue. A ViewSet is, as the name suggests, a class that provides the functionality of a set of views which are closely related. It’s one class but provides a set of views. We can handle both “collection” and “element” type of resources from the same class. And not just those, we can add even other related actions.

Since a ViewSet handles both type of resources, we can no longer think in terms of the http verbs. Because both /api/subscriber and /api/subscriber/1 can respond to  GET requests and should produce different types of response. So we can no longer work with the get, post, put etc methods. We need to think more along the actions we can take on the entity (Subscriber) as a whole. A ViewSet works with these methods instead:

• list – list all elements, serves GET to /api/subscriber
• create – create a new element, serves POST to /api/subscriber
• retrieve – retrieves one element, serves GET to /api/subscriber/1
• update and partial_update – updates single element, handles PUT/PATCH to /api/subscriber/1
• destroy – deletes single element, handles DELETE to /api/subscriber/1

Instead of our old get and post methods in separate classes, we can now define these methods in one single class and be done with it. But with general ViewSet, we have to provide logic / code for these views. That would require more time and efforts. What if, we could generate these methods from our models / querysets? Well, we can! 😀

The ModelViewSet

The ModelViewSet would only ask for the serializer class and the queryset. And then it will provide all the functionality of the different ViewSet methods. Let’s see the example:

Our SubscriberViewSet now extends the ModelViewSet and we provided the queryset and the serializer_class. Done. Really!

But there’s one slight problem, the ViewSet and ModelViewSet both handle at least two distincts url paths – /api/subscriber (the collection path) and /api/subscriber/1 – the elements path. How do we tell Django’s URLConf to route requests to both urls to our single ViewSet? Well, we have to declare those paths ourselves. We can use the as_view to both paths, defining which http verb should be routed to which methods:

Or we can simply use a Router.

Using Routers

A Router instance let’s us register our ViewSet to it and then we can just add the router.urls to our urlpatterns. It will keep track of the view sets we register and the urls property will generate all the url patterns required for those view sets to work.  Let’s add our newly created SubscriberViewSet to a router and see for ourselves. Open the api/urls.py file and create the router there and register the viewset.

That’s all that is required. Now try visiting – http://localhost:8000/api/subscribers or http://localhost:8000/api/subscribers/1 – it all works.

Fantastic, so we just generated a full RESTful API from a model with a surprisingly short amount of code! Isn’t that wonderful? Just don’t trust my words, go and look at your SubscriberViewSet or the SubscriberSerializer or the above defined router.

With the help of ModelSerializer, ModelViewSet and a router instance, we can build elegant CRUD APIs from our Django models insanely fast. At the same time, if we need, we can just override one of those methods (list, retrieve, create etc) to alter the default behavior with our own.

What’s Next?

We have crafted a nice, functional REST API. The next stop would be securing it. In our next post, we will be discussing Authentication and Permissions.

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