Hiya,
The Ajax Spider will not perform authentication for you.
You need to get authentication working in the "standard" case when you get send a request, e.g. from the Manual Request Editor and only when that is working should you look at configuration for the Ajax Spider.
If the browser does not maintain any authentication state then it should be relatively straightforward.
If it does maintain authentication state then you will need to inject that state using a selenium script.
Cheers,
Simon