sigauth

directory-signature-auth

Library implementing Hawk authentication scheme using a message authentication code (MAC) algorithm to provide partial HTTP request cryptographic verification.

The client implements RequestSigner to generate a secret-salted hash of the request URL and body. The secret-salt is shared with the target server.

The target server implements RequestSignatureChecker to check the signature provided in the request header accurately describes the request's URL and request body.

If RequestSignatureChecker accepts the header as genuine then the request is accepted, otherwise the request is rejected.

RequestSigner usage

Python requests

On the client, a signature can be generated for a requests's requests.Request:

import requests

from sigauth.utils import RequestSigner

from django.conf import settings


request_signer = RequestSigner(settings.API_SIGNATURE_SECRET)


def send_request(method, url, body):
    request = requests.Request(method=method, url=url, body=body).prepare()
    sign_request(request)
    return requests.Session().send(request)


def sign_request(request):
    headers = request_signer.get_signature_headers(
        url=request.path_url,
        body=request.body,
        method=request.method,
        content_type=request.headers.get('Content-Type'),
    )
    request.headers.update(headers)

RequestSignatureChecker usage

Django Rest Framework

This library implements a wrapper around RequestSignatureChecker for Django Rest Framework: SignatureCheckPermissionBase. It must be sub-classed to set the secret:

from sigauth import permissions

from django.conf import settings


class SignatureCheckPermission(permissions.SignatureCheckPermissionBase):
    secret = settings.SIGNATURE_SECRET

On the target server, SignatureCheckPermission can then be set in the DEFAULT_PERMISSION_CLASSES setting, or on a specific DRF view's permission_classes attribute.

Django View

On the target server, the signature checker can be implemented on views too:

from django.http import HttpResponseForbidden

from sigauth.utils import RequestSignatureChecker


api_checker = RequestSignatureChecker(settings.SIGNATURE_SECRET)


class SignatureCheckMixin:
    def dispatch(self, request, *args, **kwargs):
        if api_checker.test_signature(request) is False:
            return HttpResponseForbidden()
        return super().dispatch(request, path='', *args, **kwargs)

SignatureCheckMixin can then be used on a view to reject incoming requests that have been tampered with.

Note that in the above examples, the client's settings.API_SIGNATURE_SECRET must be the same value as api's settings.SIGNATURE_SECRET

Middleware

Some services may expect every request to require signature checks. This library implements a wrapper around RequestSignatureChecker for Django middleware to facilitate this: SignatureCheckMiddlewareBase. It must be sub-classed to set the secret:

from sigauth.middleware import SignatureCheckMiddlewareBase

from django.conf import settings

class SignatureCheckMiddleware(SignatureCheckMiddlewareBase):
    secret = settings.SIGNATURE_SECRET

SignatureCheckMiddleware can then be added to the MIDDLEWARE setting (or MIDDLEWARE_CLASSES if using Django < 2). Set SIGAUTH_URL_NAMES_WHITELIST settings to a list of url names that should be excluded from checks.

Installation

pip install -e git+https://[e-mail]/uktrade/directory-signature-auth.git@v1.0.0#egg=directory-signature-auth

Development

$ git clone https://github.com/uktrade/directory-signature-auth
$ cd directory-signature-auth
$ make

Publish to PyPI

The package should be published to PyPI on merge to master. If you need to do it locally then get the credentials from rattic and add the environment variables to your host machine:

Setting
DIRECTORY_PYPI_USERNAME
DIRECTORY_PYPI_PASSWORD

Then run the following command:

make publish