Invoking XI web service within GP process

Hi,

I have tried to setup a guided procedures process which consists among other things of the invocation of a XI web serivce. (I'm using XI 3.0 and the GP Version which comes with SP8).

Since the request of a XI web services needs authentication, I have to define a logical destination for that web service, haven't I? Or is there another (easier) possibility?

Regards,

Marc