Django for APIs is a project-based guide to building modern APIs with Django & Django REST Framework. It is suitable for beginners who have never built an API before as well as professional programmers looking for a fast-paced introduction to Django fundamentals and best practices.

These are essential notes and code snippets from the book that help in extending any existing Django website into web API with minimal effort, covering everything from scratch to hosting and API documentation. We'll be discussing the different types of user authentication methods in Part III.

Let's begin!

Read Part I and Part II

User Authentication

• Authorization: API Permissions
• Authentication: process by which a user can register for a new account, log in with it, and log out

Basic Authentication:

The most common form of HTTP authentication is known as “Basic” Authentication. When a client makes an HTTP request, it is forced to send an approved authentication credential before access is granted.

The complete request/response flow looks like this:

1. Client makes an HTTP request
2. Server responds with an HTTP response containing a 401 (Unauthorized) status code and WWW-Authenticate HTTP header with details on how to authorize
3. Client sends credentials back via the Authorization HTTP header
4. Server checks credentials and responds with either 200 OK or 403 Forbidden status code. Once approved, the client sends all future requests with the Authorization HTTP header credentials.

Note: The authorization credentials sent are the unencrypted base64 encoded version of <username>:<password>.

Cons:

• On every single request the server must look up and verify the username and password, which is inefficient.
• User credentials are being passed in clear text—not encrypted at all, can be easily captured and reused.

Note: Basic authentication should only be used via HTTPS, the secure version of HTTP.

Session Authentication:

At a high level, the client authenticates with its credentials (username/password) and then receives a session ID from the server which is stored as a _cookie). This session ID is then passed in the header of every future HTTP request.

When the session ID is passed, the server uses it to look up a session object containing all available information for a given user, including credentials. This approach is stateful because a record must be kept and maintained on both the server (the session object) and the client (the session ID).

Let’s review the basic flow:

1. A user enters their login credentials (typically username/password)
2. The server verifies the credentials are correct and generates a session object that is then stored in the database
3. The server sends the client a session ID — not the session object itself—which is stored as a cookie on the browser
4. On all future requests the session ID is included as an HTTP header and if verified by the database, the request proceeds
5. Once a user logs out of an application, the session ID is destroyed by both the client and server
6. If the user later logs in again, a new session ID is generated and stored as a cookie on the client

Note: The default setting in Django REST Framework is actually a combination of Basic Authentication and Session Authentication. Django’s traditional session-based authentication system is used and the session ID is passed in the HTTP header on each request via Basic Authentication.

Pros:

• User credentials are only sent once, not on every request/response cycle as in Basic Authentication.
• It is also more efficient since the server does not have to verify the user’s credentials each time, it just matches the session ID to the session object which is a fast look up.

Cons:

• A session ID is only valid within the browser where log in was performed; it will not work across multiple domains. This is an obvious problem when an API needs to support multiple front-ends such as a website and a mobile app.
• The session object must be kept up-to-date which can be challenging in large sites with multiple servers.
• The cookie is sent out for every single request, even those that don’t require authentication, which is inefficient.

Note: It is generally not advised to use a session-based authentication scheme for any API that will have multiple front-ends.

Token Authentication

Token-based authentication is stateless: once a client sends the initial user credentials to the server, a unique token is generated and then stored by the client as either a cookie or in local storage. This token is then passed in the header of each incoming HTTP request and the server uses it to verify that a user is authenticated.

The server itself does not keep a record of the user, just whether a token is valid or not.

Cookies vs localStorage

- Cookies are used for reading server-side information. 
They are smaller (4KB) in size and automatically sent with each HTTP request. 

- LocalStorage is designed for client-side information. 
It is much larger (5120KB) and its contents are not sent by default with each HTTP request.

Tokens stored in both cookies and localStorage are vulnerable to XSS attacks. 
The current best practice is to store tokens in a cookie with the httpOnly and Secure cookie flags.

Note: The HTTP header WWW-Authenticate specifies the use of a Token which is used in the response Authorization header request.

Pros:

• Since tokens are stored on the client, scaling the servers to maintain up-to-date session objects is no longer an issue.
• Tokens can be shared amongst multiple front-ends: the same token can represent a user on the website and the same user on a mobile app.

Cons:

• A token contains all user information, not just an id as with a session-id/session object set up. Since the token is sent on every request, managing its size can become a performance issue.

Django REST Framework's built-in TokenAuthentication:

• It doesn't support setting tokens to expire
• It only generates one token per user

JSON Web Tokens(JWTs):

JSON Web Tokens (JWTs) are a new, enhanced version of tokens that can be added to Django REST Framework via several third-party packages.

• JWTs have several benefits including the ability to generate unique client tokens and token expiration.
• They can either be generated on the server or with a third-party service like Auth0.
• And JWTs can be encrypted which makes them safer to send over unsecured HTTP connections.

Default Authentication in DRF

• DEFAULT_PERMISSION_CLASSES: AllowAny
• DEFAULT_AUTHENTICATION_CLASSES: SessionAuthentication and BasicAuthentication.

REST_FRAMEWORK = {
    'DEFAULT_PERMISSION_CLASSES': [
        'rest_framework.permissions.IsAuthenticated',
    ],
    'DEFAULT_AUTHENTICATION_CLASSES': [  # new
        'rest_framework.authentication.SessionAuthentication',
        'rest_framework.authentication.BasicAuthentication'
    ],
}

Why use both methods?

• Sessions are used to power the Browsable API and the ability to log in and log out of it.
• BasicAuthentication is used to pass the session ID in the HTTP headers for the API itself.

Implementing token authentication

The first step is to update our DEFAULT_AUTHENTICATION_CLASSES setting to use TokenAuthentication as follows:

REST_FRAMEWORK = {
    'DEFAULT_PERMISSION_CLASSES': [
        'rest_framework.permissions.IsAuthenticated',
    ],
    'DEFAULT_AUTHENTICATION_CLASSES': [
        'rest_framework.authentication.SessionAuthentication',
        'rest_framework.authentication.TokenAuthentication',  # new
    ],
}

• We keep SessionAuthentication since we still need it for our Browsable API, but now use tokens to pass authentication credentials back and forth in our HTTP headers.
• We also need to add the authtoken app which generates the tokens on the server. It comes included with Django REST Framework but must be added to our INSTALLED_- APPS setting.

'rest_framework.authtoken',

Django-Rest-Auth

To create API endpoints so user can log in, log out, and reset password.

• Install the django-rest-auth package

pip install django-rest-auth

• Add the new app to the INSTALLED_APPS config in settings.py

'rest_auth',

• Set the routes in urls.py

path('api/v1/rest-auth/', include('rest_auth.urls')), 

User Registration

Traditional Django does not ship with built-in views or URLs for user registration and neither does Django REST Framework.

A popular approach is to use the third-party package django-allauth which comes with user registration as well as a number of additional features to the Django auth system such as social authentication via Facebook, Google, Twitter, etc.

• Install the django-allauth package

pip install django-allauth

• Update the INSTALLED_APPS settings

'django.contrib.sites',
'allauth',
'allauth.account',
'allauth.socialaccount',
'rest_auth.registration',

• Make sure to also include EMAIL_BACKEND and SITE_ID.

Note: Technically it does not matter where in the settings.py file they are placed, but it’s common to add additional configs like that at the bottom.

EMAIL_BACKEND = 'django.core.mail.backends.console.EmailBackend' # new
SITE_ID = 1 # new

Note:
The email back-end config is needed since by default an email will be sent when a new user is registered, asking them to confirm their account. Rather than also set up an email server, we will output the emails to the console with the console.EmailBackend
setting.
SITE_ID is part of the built-in Django “sites” framework which is a way to host multiple websites from the same Django project. We obviously only have one site we are working on here but django-allauth uses the sites framework, so we must specify
a default setting.

• Add URL route for registration

path('api/v1/rest-auth/registration/', include('rest_auth.registration.urls')),

Read Part IV here