I have a java app with a .net application running in the java applications embedded browser.
I want the java application to call a .net WCF or web service with a username and password.
The wcf will set the user to authorized in forms authentication.
In the java desktop application I will then load a .aspx page that was protected via forms authentication.
How can I accomplish this? Is it even possible...?
You will need to enable ASP.NET compatibility mode on the WCF service in order to enable forms authentication.
The Java client application could send username and password over a secure connection and your WCF service authenticates the user via FormsAuthentication.Authenticate(username, password) or FormsAuthentication.SetAuthCookie.
You will then need to use a cookie store on the Java client side in order to pass the authentication cookie on every consecutive request (and update it when it gets refreshed), but this should be a built-in feature of your HTTP-client.
The .aspx page must run on a server with the same machine key as the WCF service.
Conclusion: Yes, it is possible, but for me it is not clear to which ".NET application" you refer to?
Edit: I think its clear now, you will need to be able to set the browser cookies. If you cant do this directly from your java application, a workaround would be to let the WCF service communicate that the user is authenticated and then set the cookie on the .aspx site request.