Optional private ssh key file

Sometimes you don't want to specify the public and private ssh key. For example: 
* You log in with the same user as the one is going to deploy and you want to passthrough your personal key.
* You log in using just password
* You may not use ssh nor password to login (this sounds stupid but may happen)

As far as I've seen both ssh proxies doesn't require the existence of keys to stablish a connection.