Approov QuickStart - Python Django Token Check

Approov is an API security solution used to verify that requests received by your backend services originate from trusted versions of your mobile apps.

This repo implements the Approov server-side request verification code in Python, which performs the verification check before allowing valid traffic to be processed by the API endpoint.

This is an Approov integration quickstart example for the Python Django framework. If you are looking for another Python integration you can check our list of quickstarts, and if you don't find what you are looking for, then please let us know here. Meanwhile, you can always use the framework agnostic quickstart example for Python, and you may find that's easily adaptable to your framework of choice.

Approov Integration Quickstart

The quickstart was tested with the following Operating Systems:

Ubuntu 20.04
MacOS Big Sur
Windows 10 WSL2 - Ubuntu 20.04

First, setup the Approov CLI.

Now, register the API domain for which Approov will issues tokens:

approov api -add api.example.com

NOTE: By default a symmetric key (HS256) is used to sign the Approov token on a valid attestation of the mobile app for each API domain it's added with the Approov CLI, so that all APIs will share the same secret and the backend needs to take care to keep this secret secure.

A more secure alternative is to use asymmetric keys (RS256 or others) that allows for a different keyset to be used on each API domain and for the Approov token to be verified with a public key that can only verify, but not sign, Approov tokens.

To implement the asymmetric key you need to change from using the symmetric HS256 algorithm to an asymmetric algorithm, for example RS256, that requires you to first add a new key, and then specify it when adding each API domain. Please visit Managing Key Sets on the Approov documentation for more details.

Next, enable your Approov admin role with:

eval `approov role admin`

For the Windows powershell:

set APPROOV_ROLE=admin:___YOUR_APPROOV_ACCOUNT_NAME_HERE___

Now, get your Approov Secret with the Approov CLI:

approov secret -get base64

Next, add the Approov secret to your project .env file:

APPROOV_BASE64_SECRET=approov_base64_secret_here

Now, add to your requirements.txt file the JWT dependency:

PyJWT==1.7.1 # update the version to the latest one

Next, you need to install the dependency:

pip3 install -r requirements.txt

Now, add the approov_middleware.py class to your project:

from django.http import JsonResponse
from os import getenv
from dotenv import load_dotenv, find_dotenv
import base64
import jwt # https://github.com/jpadilla/pyjwt/

# @link https://django.readthedocs.io/en/stable/topics/http/middleware.html
class ApproovMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

        load_dotenv(find_dotenv(), override=True)

        # Token secret value obtained with the Approov CLI tool:
        #  - approov secret -get
        approov_base64_secret = getenv('APPROOV_BASE64_SECRET')

        if approov_base64_secret == None:
            raise ValueError("Missing the value for environment variable: APPROOV_BASE64_SECRET")

        self.APPROOV_SECRET = base64.b64decode(approov_base64_secret)

    def __call__(self, request):
        approov_token_claims = self.verifyApproovToken(request)

        if approov_token_claims == None:
            return JsonResponse({}, status = 401)

        return self.get_response(request)

    # @link https://approov.io/docs/latest/approov-usage-documentation/#backend-integration
    def verifyApproovToken(self, request):
        approov_token = request.headers.get("Approov-Token")

        # If we didn't find a token, then reject the request.
        if approov_token == None:
            # You may want to add some logging here.
            return None

        try:
            # Decode the Approov token explicitly with the HS256 algorithm to avoid
            # the algorithm None attack.
            approov_token_claims = jwt.decode(approov_token, self.APPROOV_SECRET, algorithms=['HS256'])
            return approov_token_claims
        except jwt.ExpiredSignatureError as e:
            # You may want to add some logging here.
            return None
        except jwt.InvalidTokenError as e:
            # You may want to add some logging here.
            return None

Finally, to activate the Approov Middleware you just need to include it in the middleware list of your Django settings as the first one in the list:

MIDDLEWARE = [
    'YOUR_APP_NAME.approov_middleware.ApproovMiddleware',
    'django.middleware.security.SecurityMiddleware',
    # lines omitted
]

NOTE: The Approov middleware is included as the first one in the list because you don't want to waste your server resources in processing requests that don't have a valid Approov token. This approach will help your server to handle more load under a Denial of Service(DoS) attack.

Not enough details in the bare bones quickstart? No worries, check the detailed quickstarts that contain a more comprehensive set of instructions, including how to test the Approov integration.

More Information

System Clock

In order to correctly check for the expiration times of the Approov tokens is very important that the backend server is synchronizing automatically the system clock over the network with an authoritative time source. In Linux this is usually done with a NTP server.

Issues

If you find any issue while following our instructions then just report it here, with the steps to reproduce it, and we will sort it out and/or guide you to the correct path.

Useful Links

If you wish to explore the Approov solution in more depth, then why not try one of the following links as a jumping off point: