How to use a deferred to return the authentication secret when using Autobahn Wamp Cra?

Question

I'm subclassing WampCraServerProtocol (from Autobahn Python) and overriding getAuthSecret. I understand that now I can return a deferred from that method, however, when doing a simple test:

def getAuthSecret(self, authKey):        
    deferred = Deferred()
    deferred.callback("secret")
    return deferred

... I get the following error on my WampCraClientProtocol:

Authentication Error! http://api.wamp.ws/error#generic Deferred instance has no attribute '__len__' None

Ok, that alone is confusing already. Are there special requirements over the deferred that getAuthSecret returns?

Ok, moving on, based on that error, I added a (trivial) len method to the deferred I'm returning:

def getAuthSecret(self, authKey):
    #secret_deferred = self.factory.get_secret(authKey)
    deferred = Deferred()
    deferred.__len__ = lambda: 1
    deferred.callback("secret")
    return deferred

... in that case, I get:

Authentication Error! http://api.wamp.ws/error#generic unsupported operand type(s) for +: 'instance' and 'str' None

That confuses me even more. I just want to know the correct way to return a deferred from that method. (I should note that everything works perfectly if a return a plain simple string). Thanks.

Answer 1

This works for me:

https://github.com/tavendo/AutobahnPython/blob/master/examples/wamp/authentication/server.py#L72

What AutobahnPython version are you using?

Update:

v0.5.9 has a bug regarding deferred based authentication (see comments below). It was fixed on v0.5.14. Wamp Cra deferred based authentication works fine on that version.