Authenticate with a webservice

[ALI-R]

I know how to authenticate to a webservice using either of these
ways(Assuming that rService represents the webservice):

1) rService.Credentials = new
System.Net.NetworkCredential("username","password","domainName");
2)rService.Credentials = System.Net.CredentialCache.DefaultCredentials;

My question is that is there a way to authenticate to a user using
WindowsIdentity ???


Thanks for your help