if(args.Length() != 3 && args.Length() != 4) return VException("Requires a GSS context, the result from the authGSSClientResponse after authGSSClientUnwrap, optional user name and callback function");
if(args.Length() == 3 && !KerberosContext::HasInstance(args[0]) && !args[1]->IsString() && !args[2]->IsFunction()) return VException("Requires a GSS context, the result from the authGSSClientResponse after authGSSClientUnwrap, optional user name and callback function");
if(args.Length() == 4 && !KerberosContext::HasInstance(args[0]) && !args[1]->IsString() && !args[2]->IsString() && !args[2]->IsFunction()) return VException("Requires a GSS context, the result from the authGSSClientResponse after authGSSClientUnwrap, optional user name and callback function");