WCF Application Layer + Client Login

My question is about a WCF (Windows Communication Foundation) application I'm working on. I've checked a lot in internet and I've realized that WCF handles authentication through transport securi开发者_如何学JAVAty by specifying credentials in the Credentials.Username property of the client. I would just like to know how I would be able to actually show the user a log-in screen and validate credentials before setting the client credentials. What I am trying to achieve is a lo-gin behavior on the client like the one in applications like Windows Live Messenger.

I don't know if what I'm asking is kinda dumb or makes no sense, I'm a WCF starter and is really confusing since I used to work only with ASP.NET.

Also, Membership and Authorization providers are available on non-IIS hosted services? If not, how you implement this on WCF?

Thanks.

You can get the user's name and passw, set the Credentials then you can call any function. If the validation fails an exception occurs, that you should catch this exception to show an error to the user.
Here you can find a complete example: http://msdn.microsoft.com/en-us/library/aa354513.aspx