Selects a file from which the identity (private key) for public key authentication is read. The
default is ~/.ssh/identity for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa and
~/.ssh/id_rsa for protocol version 2. Identity files may also be specified on a per-host basis in
the configuration file. It is possible to have multiple -i options (and multiple identities
specified in configuration files). ssh will also try to load certificate information from the
filename obtained by appending -cert.pub to identity filenames.