Setting up SSH using key authentication

For trusted systems it is often useful to enable Passthru SSH between the
various servers. What this means is that users will be able to perform ssh
and all related operations such as scp between these servers without having
supply a password each time for a specific user defined on both systems.

To get this working follow the steps below:

For this example, we will setup a Passthu SSH connection from Box A to Box B as user testuser.
Thus Box A is the ssh client while Box B is the ssh server.

On the client (Box A) run the following command as testuser:

$ ssh-keygen -t rsa -f $HOME/.ssh/id_rsa -P ''

This should result in two files, $HOME/.ssh/id_rsa and $HOME/.ssh/id_rsa.pub. The former
file is the private encryption key and the latter is the public key.

Copy the public key id_rsa.pub to the server (Box B) and append it's contents to
$HOME/.ssh/authorized_keys as testuser.

$ cat id_rsa.pub >> $HOME/.ssh/authorized_keys
$ chmod 0600 $HOME/.ssh/authorized_keys

At this point you should be all set. All ssh commands should allow Passthru connections
from Box A to Box B as testuser.