After upgrade to Python 3.5.0a3 assertion failure results in wamp.error.cannot_authenticate

Today I installed a new Python 3.5.0a3 virtualenv and pip installed autobahn 0.10.9. I then ran an application that was working fine under Python 3.4 and got a very uniformative error:

wamp.error.cannot_authenticate:

Doing a little digging, I can see this is the message sent back in wamp/protocol.py in onMessage in the errback added to the onChallenge call.

The first problem is that no information is printed about the error. I took a look at err.value and it is an AssertionError instance. Then I imported traceback and called traceback.print_tb(err._traceback) and it showed me:

  File "/Users/terry/.virtualenvs/lm3/lib/python3.5/site-packages/txaio/aio.py", line 327, in done
    res = f.result()
  File "/usr/local/Cellar/python3/3.5.0a3/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/futures.py", line 275, in result
    raise self._exception
  File "/Users/terry/.virtualenvs/lm3/lib/python3.5/site-packages/txaio/aio.py", line 271, in as_future
    res = fun(*args, **kwargs)
  File "/Users/terry/dark-matter/light-matter/light/autobahn/component.py", line 18, in onChallenge
    challenge.extra['challenge'])
  File "/Users/terry/.virtualenvs/lm3/lib/python3.5/site-packages/autobahn/wamp/auth.py", line 235, in compute_wcs
    assert(type(challenge) == bytes)

I printed out type(challenge) and it's a str. Its value is the str representation of a dict:

{"nonce": "0Edxh609UnVkMv6X", "authprovider": "dynamic", "authid": "database", "timestamp": "2015-09-21T22:21:37.667Z", "authrole": "database", "authmethod": "wampcra", "session": 4486509142781041}

So it seems that something that used to be bytes in Python 3.4 is now a str...

It would be good if the error message actually said what went wrong, and of course good if the assertion didn't fail!

Start in wamp/protocol.py at onMessage and its onChallenge errback, then inspect autobahn/wamp/auth.py around compute_wcs and its bytes assertion. Reproduce the Python 3.5 failure and make the authentication error expose the underlying problem while handling the challenge value consistently; done means the reported authentication flow no longer fails on the shown str value.