Http-bind response value

When initiating an http-bind session, I keep getting “not authorized” failures, which I’m sure are caused by an incorrect ‘response’ value being encoded into base64.

I’ve looked at XEP-206: XMPP over BOSH, example 7, but it hasn’t helped.

Are there any examples showing how to correctly calculate the response value, or has anyone here managed to get it working?

Thanks.