User authentication to services

[Rob Taylor]

I would like to make a service on the system bus that can confirm that a message purporting to come from a user actually comes from the user. As far as I can tell dbus has the ability for an app to authenticate to a server and vice versa, but not for one app to authenticate to another app. Are there any plans for adding this kind of funtionality or should i just layer my own authentication on top of the protocol? 
As far as I can tell as I trust the server and the server knows who sent the message if i could ask the server who sent a message, i could authenicate this way, no?

Thanks,

Rob Taylor