mod_authn_otp is an Apache web server module for two-factor authentication
using one-time passwords (OTP) generated via the HOTP/OATH algorithm
defined in RFC 4226. This creates a simple way to protect a web site with
one-time passwords, using any RFC 4226-compliant hardware or software
token device. mod_authn_otp also supports the Mobile-OTP algorithm.
mod_authn_otp supports both event and time based one-time passwords. It
also supports "lingering" which allows the repeated re-use of a previously
used one-time password up to a configurable maximum linger time. This
allows one-time passwords to be used directly in HTTP authentication
without forcing the user to enter a new one-time password for every
mod_authn_otp supports both basic and digest authentication, and will
auto-synchronize with the user's token within a configurable maximum
offset (auto-synchronization is not supported with digest authentication).
mod_authn_otp is especially useful for setting up protected web sites
that require more security than simple username/password authentication
yet also don't require users to install special VPN software, and is
compatible with software tokens that run on cell phones.
Also included is otptool, a one-time password command line utility.
otptool can be used on a simple call-out basis to integrate two-factor
authentication into any existing authentication solution.