Implement Interactor.interact by opening the browser window
        and waiting for the discharge token

def interact(self, ctx, location, ir_err):
        '''Implement Interactor.interact by opening the browser window
        and waiting for the discharge token'''
        p = ir_err.interaction_method(self.kind(), WebBrowserInteractionInfo)
        if not location.endswith('/'):
            location += '/'
        visit_url = urljoin(location, p.visit_url)
        wait_token_url = urljoin(location, p.wait_token_url)
        self._open_web_browser(visit_url)
        return self._wait_for_token(ctx, wait_token_url)