@auth doesn't work in python3 because of comparison bytes with str

[ben-xo]

sign.py calls get_signature(request) and passes it to validate_multiple_signatures(), which calls make_hmac_for(key, body). Unfortunately, the signature from get_signature is a string, whilst the signature from make_hmac_for() is a byte array.

The workaround is to cast them both to byte arrays with six.b() right before the comparison, otherwise they comparison always fails.

[jamesjwarren]

Fixed in #26