I have implemented SSO with Ariba through SAML protocol. Now I hope to realize single logout (SLO), that is, log out Ariba through IDP. Can Ariba support this function?

i got a question when i use an ariba contract inbound webservice name "Download Contract Terms", the wsdl file ask me to specify "onBehalfUserId", but i dont know what this field means. I try the realm name of my ariba and my user name of ariba, both...