Public Enum RpcAuthentication 
   Inherits System.Enum

public enum RpcAuthentication : System.Enum 

Guid iid = Guid.NewGuid();
using (RpcServerApi server = new RpcServerApi(iid))
{
    server.AddProtocol(RpcProtseq.ncalrpc, "lrpctest", 5);
    server.AddAuthentication(RpcAuthentication.RPC_C_AUTHN_WINNT);
    server.StartListening();
    RpcServerApi.RpcExecuteHandler handler = 
        delegate(IRpcClientInfo client, byte[] arg)
        { return arg; };

    using (RpcClientApi client = new RpcClientApi(iid, RpcProtseq.ncalrpc, null, "lrpctest"))
    {
        client.AuthenticateAs(null, RpcClientApi.Self, RpcProtectionLevel.RPC_C_PROTECT_LEVEL_PKT_PRIVACY, RpcAuthentication.RPC_C_AUTHN_WINNT);

        server.OnExecute += handler;
        client.Execute(new byte[0]);
        
        server.OnExecute -= handler;
        try 
        {
            client.Execute(new byte[0]);
            Assert.Fail();
        }
        catch (RpcException)
        { }
    }
}

Dim iid As Guid = Guid.NewGuid()
Using server As New RpcServerApi(iid)
    server.AddProtocol(RpcProtseq.ncalrpc, "lrpctest", 5)
    server.AddAuthentication(RpcAuthentication.RPC_C_AUTHN_WINNT)
    server.StartListening()
    Dim handler As RpcServerApi.RpcExecuteHandler = Function(client As IRpcClientInfo, arg As Byte()) Do
        Return arg
    End Function

    Using client As New RpcClientApi(iid, RpcProtseq.ncalrpc, Nothing, "lrpctest")
        client.AuthenticateAs(Nothing, RpcClientApi.Self, RpcProtectionLevel.RPC_C_PROTECT_LEVEL_PKT_PRIVACY, RpcAuthentication.RPC_C_AUTHN_WINNT)

        server.OnExecute += handler
        client.Execute(New Byte(0) {})

        server.OnExecute -= handler
        Try
            client.Execute(New Byte(0) {})
            Assert.Fail()
        Catch generatedExceptionName As RpcException
        End Try
    End Using
End Using