Thanks for your response. I've tried may things but with no success so far. I tried disabling auto actions but that didn't make any difference. I tried disabling and reordering the authentication plugins but that also makes no difference.
It only gets called twice if the first call returns true so something else is happening after a successful login which is causing login to get called again. I set-up a breakpoint within the doAuthenticate function and here is a screenshot of the stack-trace each time it is called:
As you can see, login() is being called more then once. Does this provide any clues? I currently have CB set to only login using username (not using authentication plugins).
This authentication plugin works great with the Joomla login so it would be really nice if it were compatible with the CB login as well.
Thanks for your help on this!