ssh-agent user setup and on demand ssh-add

DESCRIPTION (from man page)

    ssh-agent is a program to hold private keys used for public key authentication (RSA, DSA, ECDSA).  The idea is that
    ssh-agent is started in the beginning of an X-session or a login session, and all other windows or programs are
    started as clients to the ssh-agent program.  Through use of environment variables the agent can be located and
    automatically used for authentication when logging in to other machines using ssh(1).

add the following lines to .bash_profile in the user home directory

SSHAGENT=/usr/bin/ssh-agent
SSHAGENTARGS="-s"
if [ -z "$SSH_AUTH_SOCK" -a -x "$SSHAGENT" ]; then
 eval `$SSHAGENT $SSHAGENTARGS`
 trap "kill $SSH_AGENT_PID" 0
fi