if, when you access the url in a browser, you get a little login dialog, you should see the same little login dialog in webview. if you would post the url, we could see for ourselves. we don't need your credentials. just be aware that a webview is not a browser; some things a browser supports are not supported by webview.
the server has several ways to handle authentication/authorization: in an http response header, serving its own login page, accepting your credentials in an http request header, as posted data or as part of the url. in theory, you could try them all one by one, but it's helpful to know exactly what the server is expecting, if possible.
a lot depends on what the dialog you saw looks like. if the server does not send an http response indicating that authentication is required, the b4a event is not triggered.
(in theory, that event is supposed to trigger a little homemade login dialog. b4a shortens the process by simply returning the id and password as a string array. if you were writing an app for the world where every user had her own login, then you would need to write the dialog yourself. follow?)
if the server is handling the authentication with its own login page, then, basically, you have to fill it in (at least the first time you visit the url in the same session).