IPrincipal 와 Identity

    // Summary:
    //     Defines the basic functionality of a principal object.
    [ComVisible(true)]
    public interface IPrincipal
    {
        // Summary:
        //     Gets the identity of the current principal.
        //
        // Returns:
        //     The System.Security.Principal.IIdentity object associated with the current
        //     principal.
        IIdentity Identity { get; }
 
        // Summary:
        //     Determines whether the current principal belongs to the specified role.
        //
        // Parameters:
        //   role:
        //     The name of the role for which to check membership.
        //
        // Returns:
        //     true if the current principal is a member of the specified role; otherwise,
        //     false.
        bool IsInRole(string role);
    }

Identity 인터페이스 

 // Summary:
    //     Defines the basic functionality of an identity object.
    [ComVisible(true)]
    public interface IIdentity
    {
        // Summary:
        //     Gets the type of authentication used.
        //
        // Returns:
        //     The type of authentication used to identify the user.
        string AuthenticationType { get; }
        //
        // Summary:
        //     Gets a value that indicates whether the user has been authenticated.
        //
        // Returns:
        //     true if the user was authenticated; otherwise, false.
        bool IsAuthenticated { get; }
        //
        // Summary:
        //     Gets the name of the current user.
        //
        // Returns:
        //     The name of the user on whose behalf the code is running.
        string Name { get; }
    }

출처 : http://man.ddvip.com/web/bsaspnetapp/LiB0019.html