Just to make sure we're talk about the same thing: You are trying to call vCO workflows from outside, using vCO's REST API and the provided Java client libraries from https://yourvcoserver:8281/api/docs. Righty?
(@Christian: Then your code doesn't fit to the topic. But it's a great example for using the vCO REST Plugin anyway, thanks for sharing! Image may be NSFW.
Clik here to view.)
I don't have a SSO example. But have you tried the HTTP Basic Authentication, as Christophe mentioned?
Cheers,
Joerg