The ssh-agent protocol allows the usage of keys and certs added to a given agent to be constrained in certain ways. The only constraints currently supported are lifetime (keys expire after some number of seconds) and confirmation (the agent requires user confirmation before performing any operations with the private key). Change-Id: Idba5760db929805bf3da43fdcaca53ae6c479ca4 Reviewed-on: https://go-review.googlesource.com/12260 Reviewed-by: Adam Langley <agl@golang.org> Run-TryBot: Adam Langley <agl@golang.org> Reviewed-by: Peter Moody <pmoody@uber.com>