Unlocking the Mystery of Session Persistence Issue Between Two Django Projects Using Both JWT and Session Authentication

When working with multiple Django projects that utilize both JWT and session authentication, you may encounter a pesky session persistence issue. This problem can leave you scratching your head, wondering why your sessions aren’t being persisted across projects. Fear not, dear developer, for we’re about to embark on a journey to solve this enigma and ensure your sessions persist like a charm!

Understanding the Problem

Before we dive into the solution, let’s take a step back and understand the issue. Imagine you have two separate Django projects, Project A and Project B. Both projects use JWT (JSON Web Token) for authentication, but they also require session authentication for specific features. You’ve implemented authentication correctly, but when a user logs in to Project A and then navigates to Project B, their session isn’t persisted. Why is this happening?

The reason lies in how Django handles sessions. By default, Django uses a cookie-based session system, where the session ID is stored on the client-side in a cookie named `sessionid`. When a user logs in to Project A, a new session is created, and the session ID is stored in the `sessionid` cookie. However, when the user navigates to Project B, the `sessionid` cookie is not sent along, causing the session to be lost.

The Solution: Implementing a Shared Session Store

To overcome this issue, we need to implement a shared session store between the two projects. One way to achieve this is by using a database-backed session store. We’ll create a new Django app that will act as a session store, and both Project A and Project B will use this app to store and retrieve sessions.

Let’s create a new Django app called `shared_sessions`:

python manage.py startapp shared_sessions

In the `shared_sessions` app, create a new model to store sessions:

from django.db import models

class Session(models.Model):
    session_key = models.CharField(max_length=40, primary_key=True)
    session_data = models.TextField()
    expire_date = models.DateTimeField(db_index=True)

    def __str__(self):
        return self.session_key

In the `shared_sessions` app’s `views.py`, create a view to handle session storage and retrieval:

from django.http import HttpRequest, HttpResponse
from django.shortcuts import get_object_or_404
from .models import Session

def get_session(request: HttpRequest, session_key: str) -> HttpResponse:
    session = get_object_or_404(Session, session_key=session_key)
    return HttpResponse(session.session_data)

def create_session(request: HttpRequest, session_data: str) -> HttpResponse:
    session = Session(session_key=request.GET.get('session_key'), session_data=session_data)
    session.save()
    return HttpResponse('Session created successfully')

In both Project A and Project B, add the `shared_sessions` app to the `INSTALLED_APPS` list in `settings.py`:

INSTALLED_APPS = [
    # ...
    'shared_sessions',
    # ...
]

Configure the `SESSION_ENGINE` setting in both projects to use the `shared_sessions` app:

SESSION_ENGINE = 'shared_sessions.sessions'

In both projects, create a new file `sessions.py` to define the custom session store:

from django.contrib.sessions.backends.db import SessionStore as DBStore
from shared_sessions.models import Session

class SessionStore(DBStore):
    def __init__(self, request):
        super().__init__(request)
        self.request = request

    def save(self, must_create=False):
        s = Session(session_key=self.session_key, session_data=self.encode(self._get_session(no_load=must_create)))
        s.save()
        return s.session_key

In both projects, update the `MIDDLEWARE` setting in `settings.py` to use the custom session store:

MIDDLEWARE = [
    # ...
    'shared_sessions.sessions.SessionStore',
    # ...
]

Implementing JWT Authentication

Now that we have a shared session store, let’s implement JWT authentication in both Project A and Project B.

In both projects, create a new file `jwt.py` to define the JWT settings:

import jwt
from django.conf import settings

def create_jwt_token(user):
    payload = {
        'user_id': user.id,
        'username': user.username,
        'exp': datetime.utcnow() + timedelta(days=7)
    }
    return jwt.encode(payload, settings.SECRET_KEY, algorithm='HS256')

def authenticate_jwt_token(token):
    try:
        payload = jwt.decode(token, settings.SECRET_KEY, algorithms=['HS256'])
        user = User.objects.get(id=payload['user_id'])
        return user
    except jwt.ExpiredSignatureError:
        return None
    except jwt.InvalidTokenError:
        return None

In both projects, create a new view to handle JWT authentication:

from django.http import HttpResponse, JsonResponse
from .jwt import create_jwt_token, authenticate_jwt_token
from django.contrib.auth.models import User

def login_view(request):
    if request.method == 'POST':
        username = request.POST.get('username')
        password = request.POST.get('password')
        user = authenticate(username=username, password=password)
        if user is not None:
            token = create_jwt_token(user)
            return JsonResponse({'token': token})
    return HttpResponse('Invalid credentials')

In both projects, update the `views.py` file to include the JWT authentication view:

from django.urls import path
from .views import login_view

urlpatterns = [
    path('login/', login_view, name='login'),
    # ...
]

Configuring the Projects

Now that we have implemented the shared session store and JWT authentication, let’s configure both Project A and Project B to use these features.

In both projects, update the `settings.py` file to include the following settings:

SESSION_COOKIE_DOMAIN = '.example.com'
CSRF_COOKIE_DOMAIN = '.example.com'

JWT_SECRET_KEY = 'your_secret_key_here'

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

AUTH_MIDDLEWARE = [
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'shared_sessions.sessions.SessionStore',
]

In both projects, update the `urls.py` file to include the following URL patterns:

from django.urls import path, include

urlpatterns = [
    path('', include('shared_sessions.urls')),
    path('api/', include('api.urls')),
    # ...
]

Testing the Solution

Now that we’ve implemented the shared session store and JWT authentication, let’s test the solution.

In Project A, log in to the system using the JWT authentication view:

curl -X POST \
  http://project-a.example.com/login/ \
  -H 'Content-Type: application/json' \
  -d '{"username": "user1", "password": "password1"}'

You should receive a JWT token in response:

{"token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyX2lkIjoxLCJ1c2VybmFtZSI6InVzZXIxIiwiZXhwIjoxNjIxNDgyMDAwfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c"}

In Project B, use the same JWT token to authenticate the user:

curl -X GET \
  http://project-b.example.com/api/protected/ \
  -H 'Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyX2lkIjoxLCJ1c2VybmFtZSI6InVzZXIxIiwiZXhwIjoxNjIxNDgyMDAwfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c' \
  -H 'Content-Type: application/json'

If everything is configured correctly, you should receive a successful response from Project B.

Conclusion

In this article, we’ve successfully implemented a shared session store between two Django projects using both JWT and session authentication. By using a database-backed session store and configuring both projects to use the same session store, we’ve ensured that sessions persist across projects. Additionally, we’ve implemented JWT authentication to provide an additional layer of security.

By following the steps outlined in this article, you should be able to resolve the session persistence issue between your Django projects and provide a seamless experience for your users.

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