With this Bzr revision from yesterday, support for Trusted Prompt Sessions have been added on the Mir side.
According to the Ubuntu Wiki, this feature comes down to "the main purpose of a trusted prompt session (TPS) then is to tie together the [application requesting access to a resource via a trusted helper, the trusted helper, and a trust prompt provider] components mentioned before, both in terms of presenting the final prompt to the user and in terms of lifecycle/focus mgmt. (from a shell's perspective). In this respect, a temporary, virtual app is introduced that spans across all three components."
Those interested in more information on this forthcoming Ubuntu security feature using Mir, see the Ubuntu Wiki.