The [pam_ssh_agent_auth][0] PAM module authenticates users using keys in
their SSH agent. Using SSH agent forwarding, it can even authenticate
users with keys on a remote system. By adding it to the PAM stack for
`sudo`, we can configure the latter to authenticate users without
requiring a password. For servers especially, this is significantly
more secure than configuring `sudo` not to require a password, while
still being almost as convenient.
For this to work, users need to enable SSH agent forwarding on their
clients, and their public keys have to be listed in the
`/etc/security/sudo.authorized_keys` file. Additionally, although the
documentation suggests otherwise, the `SSH_AUTH_SOCK` environment
variable has to be added to the `env_keep` list in *sudoers(5)*.
[0]: https://github.com/jbeverly/pam_ssh_agent_auth
Dustin