Stuff that's missing from the Facebook python SDK

fb_helpers.py

import base64
import hashlib
import hmac
import simplejson as json

def base64_url_decode(inp):
    padding_factor = (4 - len(inp) % 4) % 4
    inp += "="*padding_factor 
    return base64.b64decode(unicode(inp).translate(dict(zip(map(ord, u'-_'), u'+/'))))

def parse_signed_request(signed_request, secret):
    if not signed_request or not secret:
        return None

    l = signed_request.split('.', 2)
    encoded_sig = l[0]
    payload = l[1]

    sig = base64_url_decode(encoded_sig)
    data = json.loads(base64_url_decode(payload))

    if data.get('algorithm').upper() != 'HMAC-SHA256':
        log.error('Unknown algorithm')
        return None
    else:
        expected_sig = hmac.new(secret, msg=payload, digestmod=hashlib.sha256).digest()

    if sig != expected_sig:
        return None
    else:
        log.debug('valid signed request received..')
        return data

def oauth_token(signed_request, secret):
    """Grab the Facebook auth token, return it or None."""
    data = parse_signed_request(signed_request, secret)
    if data and isinstance(data, dict) and data.has_key('oauth_token'):
        return data['oauth_token']

def oauth_URL(**args):
    """Crafts a oauth link that you can send users to if you want to
    get an auth_token or obtain more permissions.
    E.G. oauth_URL(scope="offline_access,friends_birthday")
    """
    return "https://graph.facebook.com/oauth/authorize?" + urllib.urlencode(args)