SSH Agent Forwarding for "sudo su"

Exporting of SSH_AUTH_SOCK environment variable when using sudo su enables forwarding of user's SSH agent connection to root environment
(umask 0440; echo 'Defaults env_keep += "SSH_AUTH_SOCK"' > /etc/sudoers.d/ssh-auth-sock)
Example of using /etc/sudoers.d/ssh-auth-sock on host machine. The example assumes that the user copied already their public SSH key to the destination machines under root user:
$ ssh -A user@host
[user@host]$ sudo su
[root@host]# ssh remote