Signed header requests python3 refactoring

[jfarcher]

While trying to refactor a script of ours which is based upon the following sample code:
https://github.com/janrain/Janrain-Sample-Code/blob/master/signed-header-requests/signed-request.py

I have updated the hmac.new to ensure the passed data is in the byte format as required, however errors are returned:
code: 431
error: signature_does_not_match
error_description: The request signature we calculated does not match the signature you provided

key=bytes(secret, 'UTF-8')
message=bytes(str_to_sign, 'UTF-8')
hashed_str = b64encode(hmac.new(key, message, sha1).digest())

Please could you advise on the best steps to be taking on upgrading to python 3?

[jfarcher]

Fixed with #28