macauthlib: library for implementing MAC Access Authentication

This is a low-level library for implementing MAC Access Authentication, a simple HTTP request-signing scheme described in:

http://tools.ietf.org/html/draft-ietf-oauth-v2-http-mac-01

To access resources using MAC Access Authentication, the client must have obtained a set of MAC credentials including an id and a secret key. They use these credentials to make signed requests to the server.

When accessing a protected resource, the server will generate a 401 challenge response with the scheme "MAC" as follows:

> GET /protected_resource HTTP/1.1
> Host: example.com

< HTTP/1.1 401 Unauthorized
< WWW-Authenticate: MAC

The client will use their MAC credentials to build a request signature and include it in the Authorization header like so:

> GET /protected_resource HTTP/1.1
> Host: example.com
> Authorization: MAC id="h480djs93hd8",
>                    ts="1336363200",
>                    nonce="dj83hs9s",
>                    mac="bhCQXTVyfj5cmA9uKkPFx1zeOXM="

< HTTP/1.1 200 OK
< Content-Type: text/plain
<
< For your eyes only:  secret data!

This library provices the low-level functions necessary to implement such an authentication scheme. For MAC Auth clients, it provides the following function:

• sign_request(req, id, key, hashmod=sha1): sign a request using MAC Access Auth.

For MAC Auth servers, it provides the following functions:

• get_id(req): get the claimed MAC Auth id from the request.
• check_signature(req, key, hashmod=sha1): check that the request was signed with the given key.

The request objects passed to these functions can be any of a variety of common object types:

• a WSGI environment dict
• a webob.Request object
• a requests.Request object
• a string or file-like object of request data

A typical use for a client program might be to install the sign_request function as an authentication hook when using the requests library, like this:

import requests
import functools
import macauthlib

# Hook up sign_request() to be called on every request.
def auth_hook(req):
    macauthlib.sign_request(req, id="<AUTH-ID>", key="<AUTH-KEY>")
    return req
session = requests.session(hooks={"pre_request": auth_hook})

# Then use the session as normal, and the auth is applied transparently.
session.get("http://www.secret-data.com/get-my-data")

A typical use for a server program might be to verify requests using a WSGI middleware component, like this:

class MACAuthMiddleware(object):

    # ...setup code goes here...

    def __call__(self, environ, start_response):

        # Find the identity claimed by the request.
        id = macauthlib.get_id(environ)

        # Look up their secret key.
        key = self.SECRET_KEYS[id]

        # If the signature is invalid, error out.
        if not macauthlib.check_signature(environ, key):
            start_response("401 Unauthorized",
                           [("WWW-Authenticate", "MAC")])
            return [""]

        # Otherwise continue to the main application.
        return self.application(environ, start_response)