Posted in Python, Tech

Django Custom Middleware

A Custom middleware can validate each http request for the set of instructions given in the middleware, before sending back a response. Let us see how we can write a custom Middleware. As an example, we will be implementing a custom Authentication Middleware here.

Django’s out-of-the box Authentication middleware only authenticates requests if the project has made use of the Django provided “User” model or has extended the same. If we have otherwise implemented a model from scratch for the user data, we will have to write a custom middleware for authentication and authorization.

I am implementing this in my twitter clone project, where I have used a custom model for user data. The details of the project can be found in my previous blogpost: Building a Twitter Clone with Django REST Framework – I

First, we will create a file in TUser App. We will call it AuthMiddleware.py. To start off, there are a few basic rules to be followed while defining a Middleware are:

  1. The custom middleware must accept a get_response argument while defining the __init__ method. This is called only once when the web server starts.
  2. Define the __call__() method. This is called each time a request is made.
  3. Include the path of the above file in settings.py – in the “Middleware” section

This is how a sample middleware is defined:

#AuthMiddleware.py
from django.contrib.auth.backends import BaseBackend

class AuthMiddleware(BaseBackend):
    def __init__(self, get_response):
        self.get_response = get_response
    def __call__(self, request):
        return self.get_response(request)
    def CustomMiddleware(self,requst):
        #Steps to perform
        return True

#settings.py
MIDDLEWARE = [
    ...
    #custom middlewares:
    'TUsers.AuthMiddleware.AuthMiddleware'
]

Here’s my version of Custom Authentication Middleware – AuthMiddleware.py

class AuthMiddleware(BaseBackend):
    def __init__(self, get_response):
        self.get_response = get_response
    def __call__(self, request):
        self.auth(request)
        return self.get_response(request)
    def auth(self,request):
        exclusion_list = ['/signup','/login']
        if request.path not in exclusion_list:
            try:
                urlstr = request.path
                user = urlstr.split('/')[1]
                token = request.session.get('authtoken').get('token')
                payload = jwt.decode(token,settings.AUTH_TOKEN)
                userObj = TUser.objects.get(username=user)
                if payload.get('username') == userObj.username:
                    return True
                else:
                    raise PermissionDenied
            except (jwt.ExpiredSignature, jwt.DecodeError, jwt.InvalidTokenError) as e:
                error = {'Error_code': status.HTTP_403_FORBIDDEN,
                                'Error_Message': "Token is Invalid/Expired"}
                logger.error(e)
                raise PermissionDenied(error)
            except Exception as e:
                error = {'Error_code': status.HTTP_403_FORBIDDEN,
                                'Error_Message': "Invalid User"}
                logger.error(e) 
                raise PermissionDenied(error) 
        else:
            return True

This middleware will automatically validates each and every request made. In this project, the validation is performed to check if the token that a user obtains while Login is valid. If yes, the API end-point performs its action and returns the intended response. If not, an exception is raised and the access to the API is forbidden.

The complete file is available on github:

https://github.com/shilpavijay/TwitterClone/blob/main/TUsers/AuthMiddleware.py

You can find the complete project code here:

https://github.com/shilpavijay/TwitterClone

Author:

https://kriyavikalpa.com/

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