requests-http-signature: A Requests auth module for HTTP Signature

requests-http-signature is a Requests authentication plugin (requests.auth.AuthBase subclass) implementing the IETF HTTP Message Signatures draft standard.

Installation

$ pip install requests-http-signature

Usage

import requests
from requests_http_signature import HTTPSignatureAuth, algorithms

preshared_key_id = 'squirrel'
preshared_secret = b'monorail_cat'
url = 'https://example.com/'

auth = HTTPSignatureAuth(key=preshared_secret,
                         key_id=preshared_key_id,
                         signature_algorithm=algorithms.HMAC_SHA256)
requests.get(url, auth=auth)

By default, only the Date header and the @method, @authority, and @target-uri derived component identifiers are signed for body-less requests such as GET. The Date header is set if it is absent. In addition, the Authorization header is signed if it is present, and for requests with bodies (such as POST), the Content-Digest header is set to the SHA256 of the request body using the format described in the IETF Digest Fields draft and signed. To add other headers to the signature, pass an array of header names in the covered_component_ids keyword argument. See the API documentation for the full list of options and details.

Verifying responses

The class method HTTPSignatureAuth.verify() can be used to verify responses received back from the server:

class MyKeyResolver:
    def resolve_public_key(self, key_id):
        assert key_id == 'squirrel'
        return 'monorail_cat'

response = requests.get(url, auth=auth)
verify_result = HTTPSignatureAuth.verify(response,
                                         signature_algorithm=algorithms.HMAC_SHA256,
                                         key_resolver=MyKeyResolver())

More generally, you can reconstruct an arbitrary request using the Requests API and pass it to verify():

request = requests.Request(...)  # Reconstruct the incoming request using the Requests API
prepared_request = request.prepare()  # Generate a PreparedRequest
HTTPSignatureAuth.verify(prepared_request, ...)

To verify incoming requests and sign responses in the context of an HTTP server, see the flask-http-signature and http-message-signatures packages.

See what is signed

It is important to understand and follow the best practice rule of "See what is signed" when verifying HTTP message signatures. The gist of this rule is: if your application neglects to verify that the information it trusts is what was actually signed, the attacker can supply a valid signature but point you to malicious data that wasn't signed by that signature. Failure to follow this rule can lead to vulnerability against signature wrapping and substitution attacks.

In requests-http-signature, you can ensure that the information signed is what you expect to be signed by only trusting the data returned by the verify() method:

verify_result = HTTPSignatureAuth.verify(message, ...)

See the API documentation for full details.

Asymmetric key algorithms

To sign or verify messages with an asymmetric key algorithm, set the signature_algorithm keyword argument to algorithms.ED25519, algorithms.ECDSA_P256_SHA256, algorithms.RSA_V1_5_SHA256, or algorithms.RSA_PSS_SHA512.

For asymmetric key algorithms, you can supply the private key as the key parameter to the HTTPSignatureAuth() constructor as bytes in the PEM format, or configure the key resolver as follows:

with open('key.pem', 'rb') as fh:
    auth = HTTPSignatureAuth(signature_algorithm=algorithms.RSA_V1_5_SHA256,
                             key=fh.read(),
                             key_id=preshared_key_id)
requests.get(url, auth=auth)

class MyKeyResolver:
    def resolve_public_key(self, key_id: str):
        return public_key_pem_bytes[key_id]

    def resolve_private_key(self, key_id: str):
        return private_key_pem_bytes[key_id]

auth = HTTPSignatureAuth(signature_algorithm=algorithms.RSA_V1_5_SHA256,
                         key=fh.read(),
                         key_resolver=MyKeyResolver())
requests.get(url, auth=auth)

Digest algorithms

To generate a Content-Digest header using SHA-512 instead of the default SHA-256, subclass HTTPSignatureAuth as follows:

class MySigner(HTTPSignatureAuth):
    signing_content_digest_algorithm = "sha-512"

Links

• Project home page (GitHub)
• Package documentation
• Package distribution (PyPI)
• Change log
• http-message-signatures - a dependency of this library that handles much of the implementation
• IETF HTTP Signatures draft

Bugs

Please report bugs, issues, feature requests, etc. on GitHub.

License

Licensed under the terms of the Apache License, Version 2.0.