When using ssh-agent I really want all keys that are added to it to have a lifetime of just x seconds (60 in my case) to prevent me from accidentally adding a key for the lifetime of ssh-agent and thus risk compromising it when I login to a compromised machine without knowing so.

Of course I already only enable forwarding when I need to, but it would be a really nice second line of defense when I also have to add the key in question to ssh-agent when I need to.

There is already 'ssh-agent -t 60 ~/.ssh/some_key' and there is also 'ssh-agent -t 60' - but as far as I can figure out there is no value that I can set in my ~/.ssh/config that will ensure that this is set.

And that's what I want.