tree bd9006a90be238ae1fbd288d02d8d8cee03d0f2e
parent af6cccc21414d6ebb2b1b41cbe5acdfac282531b
author Suharsh Sivakumar <suharshs@google.com> 1431971854 -0700
committer Suharsh Sivakumar <suharshs@google.com> 1431973669 +0000

cmd/principal,services/identity: Propagate cancellation and errors
from identity server to principal tool.

This change does the following:
(1) Clicking the cancel button at the addcaveats page sends a cancel
    error to the identity server.
(2) All errors encountered after a toolRedirectURL is decoded are
    propagated to that url.
(3) If the principal tool recieves a identity server error, it will
    not attempt to seek a blessings.

This ensure that cancelling a auth flow doesn't leave the principal
tool hanging, and clearly tells the user that they were successful
in their cancellation.

address vanadium/issues#492

Change-Id: Ia142161bcd85bf5d84971e64d7d645ff98d49bfb