LOGIN_DUO(8) BSD System Manager's Manual LOGIN_DUO(8)NAMElogin_duo — second-factor authentication via Duo login service
SYNOPSISlogin_duo [-d] [-c file] [-h host] [-f user] [command [args...]]
DESCRIPTIONlogin_duo provides secondary authentication via the Duo authentication
service, executing the user's login shell or command only if successful.
The following options are available:
-c Specify an alternate configuration file to load. Default is
/usr/local/etc/duo/login_duo.conf
-d Debug mode; send logs to stderr instead of syslog.
-h Specify the remote IP address for this login (normally taken
from the SSH_CONNECTION environment variable, if set).
-f Specify an alternate Duo user to authenticate as.
If login_duo is installed setuid root (the default), these options are
only available to the super-user.
After successful Duo authentication, the user's login shell is invoked,
or if an alternate command or SSH_ORIGINAL_COMMAND environment variable
is specified, it will be executed via the user's shell with a -c option.
CONFIGURATION
The INI-format configuration file must have a “duo” section with the fol‐
lowing options:
host Duo API host (required).
ikey Duo integration key (required).
skey Duo secret key (required).
groups If specified, Duo authentication is required only for users
whose primary group or supplementary group list matches one of
the space-separated pattern-lists (see PATTERNS below).
failmode On service or configuration errors that prevent Duo authentica‐
tion, fail “safe” (allow access) or “secure” (deny access).
Default is “safe”.
pushinfo Send command to be approved via Duo Push authentication.
Default is “no”.
http_proxy
Use the specified HTTP proxy, same format as the HTTP_PROXY
environment variable.
autopush Upon successful first-factor authentication, automatically send
a login request to the primary second-factor (usually Duo
Push). Can be “yes” or “no”. Default is “no”.
motd Print the contents of /usr/local/etc/motd to screen after a
successful login. Either "yes" or "no." Default is "no".
prompts Number of login attempts a user gets. Default is 3. If using
autopush, it is recommended to set prompts to 1.
accept_env_factor
Look for factor selection or passcode in the DUO_PASSCODE envi‐
ronment variable, before prompting the user. Can override auto‐
push. Default is "no".
fallback_local_ip
If unable to determine the authentication users's IP address,
fallback on the IP address of the server. Default is "no".
https_timeout
Set to the number of seconds to wait for HTTPS responses from
Duo Security. If Duo Security takes longer than the configured
number of seconds to respond to the preauth API call, the con‐
figured failmode is triggered. Other network operations such as
DNS resolution, TCP connection establishment, and the SSL hand‐
shake have their own independent timeout and retry logic.
Default is 0, which disables the HTTPS timeout.
An example configuration file:
[duo]
host = api-deadbeef.duosecurity.com
ikey = SI9F...53RI
skey = 4MjR...Q2NmRiM2Q1Y
pushinfo = yes
autopush = yes
If installed setuid root (the default), login_duo performs Duo authenti‐
cation as a dedicated privilege separation user, requiring that the con‐
figuration file be owned and readable only by this user.
PATTERNS
A pattern consists of zero or more non-whitespace characters, ‘*’ (a
wildcard that matches zero or more characters), or ‘?’ (a wildcard that
matches exactly one character).
A pattern-list is a comma-separated list of patterns. Patterns within
pattern-lists may be negated by preceding them with an exclamation mark
(‘!’). For example, to specify Duo authentication for all users (except
those that are also admins), and for guests:
groups = users,!wheel,!*admin guests
EXAMPLESlogin_duo can be enabled system-wide by specifying its full path as a
ForceCommand in sshd_config(5) to capture any SSH remote login (including
subsystems, remote commands, and interactive login):
ForceCommand /usr/local/sbin/login_duo
Similarly, a group of administrators could require two-factor authentica‐
tion for login to a shared root account by specifying login_duo as the
forced command for each public key in ~root/.ssh/authorized_keys:
command="/usr/local/sbin/login_duo -f alice"
ssh-rsa AAAAB2...19Q== alice@example.net
command="/usr/local/sbin/login_duo -f bob"
ssh-dss AAAAC3...51R== bob@example.net
A user without root access could configure their own account to require
Duo authentication via the same ~/.ssh/authorized_keys forced command
mechanism and a user-installed (non-setuid) login_duo.
FILES
/usr/local/etc/duo/login_duo.conf
Default configuration file path
AUTHORSlogin_duo was written by Duo Security ⟨support@duosecurity.com⟩
NOTES
When used to protect remote SSH access, only interactive sessions support
interactive Duo login. For scp(1), sftp(1), rsync(1), and other ssh(1)
remote commands, login_duo automatically tries the user's default out-of-
band factor (smartphone push or voice callback) and disables real-time
login progress reporting to provide a clean shell environment.
BSD September 3, 2010 BSD
