Since the earliest days of WebCopy, it has supported challenge authentication (where a web browser prompts you for credentials) and form based authentication (where you enter credentials into a web page). Almost all web sites use the latter approach and with WebCopy this can either be tricky to configure or impossible due to websites using interactive methods such as authenticators or captcha codes.
In order to resolve this, WebCopy 1.7 includes a new option named Log in use web browser, found in the Passwords property page.
When this new option is set, WebCopy will display a browser window when you copy a website to allow you to authenticate with the web site. Once authenticated, the cookies associated with the site are applied to WebCopy's crawler and copying will commence.
You can learn more about this feature and any caveats on the documentation page.