ASIHTTPRequest: when does ASIAuthenticationDialog appear?

When does the authentication dialog app开发者_JAVA百科ear? If I didn't set the username/password in the request or URL?

I believe it'll appear if the http server returns a HTTP 401 response code and there is no username/password otherwise available for asihttprequest to use. (ie. there's no username/password in the url, nor set on the request, not present in the keychain, nor already used in this session, nor available from a delegate.)