pam_ssh_agent_auth8

Overview

This module provides authentication via ssh-agent. If an ssh-agent listening at SSH_AUTH_SOCK can successfully authenticate that it has the secret key for a public key in the specified file, authentication is granted, otherwise authentication fails.

Configuration

/etc/pam.d/sudo: auth sufficient pam_ssh_agent_auth.so file=/etc/security/authorized_keys

/etc/sudoers:

In older versions of sudo (< 1.8.5) it was necessary to set:
Defaults env_keep += "SSH_AUTH_SOCK"

This configuration would permit anyone who has an SSH_AUTH_SOCK that manages the private key matching a public key in /etc/security/authorized_keys to execute sudo without having to enter a password. Note that the ssh-agent listening to SSH_AUTH_SOCK can either be local, or forwarded.

Unlike NOPASSWD, this still requires an authentication, it's just that the authentication is provided by ssh-agent, and not password entry.

Arguments

file=<path to authorized_keys>

Specify the path to the authorized_keys file(s) you would like to use for authentication. Subject to tilde and % EXPANSIONS (below)

allow_user_owned_authorized_keys_file

A flag which enables authorized_keys files to be owned by the invoking user, instead of root. This flag is enabled automatically whenever the expansions %h or ~ are used.

authorized_keys_command=<path to executable>

Specify an external command to run, which should take a single argument, the username of the person being authenticated, and emit to its stdout a file in authorized_keys format. This is ideally suited for use with sssd's sss_ssh_authorizedkeys, for authenticating users via authorized_keys stored in ldap or other sssd supported security service.

authorized_keys_command_user=<username>

Specify a user to run the authorized_keys_command as. If this option is not specified, the authorized_keys_command will be run as the user being authenticated.

debug

A flag which enables verbose logging

sudo_service_name=<service name you compiled sudo to use>

(when compiled with --enable-sudo-hack)

Specify the service name to use to identify the service "sudo". When the PAM_SERVICE identifier matches this string, and if PAM_RUSER is not set, pam_ssh_agent_auth will attempt to identify the calling user from the environment variable SUDO_USER.

This defaults to "sudo".

Expansions

~ -- same as in shells, a user's Home directory

Automatically enables allow_user_owned_authorized_keys_file if used in the context of ~/. If used as ~user/, it would expect the file to be owned by 'user', unless you explicitly set allow_user_owned_authorized_keys_file

%h -- User's Home directory

Automatically enables allow_user_owned_authorized_keys_file

%H -- The short-hostname

%u -- Username

%f -- FQDN

Examples

in /etc/pam.d/sudo

"auth sufficient pam_ssh_agent_auth.so file=~/.ssh/authorized_keys"

The default .ssh/authorized_keys file in a user's home-directory

"auth sufficient pam_ssh_agent_auth.so file=%h/.ssh/authorized_keys"

Same as above.

"auth sufficient pam_ssh_agent_auth.so file=~fred/.ssh/authorized_keys"

If the home-directory of user 'fred' was /home/fred, this would expand to /home/fred/.ssh/authorized_keys. In this case, we have not specified allow_user_owned_authorized_keys_file, so this file must be owned by 'fred'.

"auth sufficient pam_ssh_agent_auth.so file=/secure/%H/%u/authorized_keys allow_user_owned_authorized_keys_file"

On a host named foobar.baz.com, and a user named fred, would expand to /secure/foobar/fred/authorized_keys. In this case, we specified allow_user_owned_authorized_keys_file, so fred would be able to manage that authorized_keys file himself.

"auth sufficient pam_ssh_agent_auth.so file=/secure/%f/%u/authorized_keys"

On a host named foobar.baz.com, and a user named fred, would expand to /secure/foobar.baz.com/fred/authorized_keys. In this case, we have not specified allow_user_owned_authorized_keys_file, so this file must be owned by root.

"auth [success=3 default=ignore] pam_ssh_agent_auth.so file=~/.ssh/authorized_keys debug"

This pam.d config format allows for more control over how pam handles success and failure. In this example, we use success=3, which specifies that when this module succeeds, pam should jump over the next 3 auth modules and continue from there. This is useful, for instance, if /etc/pam.d/common-auth is included, and contains 3 "auth required" or similar module rules that we wish to skip, but we wish not to skip other auth rules.

For more information, please see http://linux.die.net/man/5/pam.d