sign.py

def import_jwk(jwk):
    """
    Used to import a JWK key from the JSON client.
    """
    if (jwk.get('kty') != 'RSA'):
        raise ValueError('Expected kty to be RSA')

    def decode_base64(data):
        # Python is very particular about padding of base64 strings. We'll
        # just pad the end with zero length data
        missing_padding = len(data) % 4
        data += '=' * (4 - missing_padding)
        # Isn't it amazing that we can read a BigInt this easy with Python!
        return int.from_bytes(
            base64.urlsafe_b64decode(data),
            byteorder='big',
            signed=False
        )

    def get_component(component):
        if component in jwk:
            return decode_base64(jwk[component])
        return None

    # In the order that they are expected by construct
    components = map(get_component, ['n', 'e', 'd', 'p', 'q', 'u'])

    # Only include components up until we have seen one which is None
    return RSA.construct(list(takewhile(lambda x: x is not None, components)))