hook pam to authenticate users against anything
Apache LDAP Directory Manager
Token based authentication module for angular.js
NTLMv2 authentication library and filter for Java
Two-factor authentication system
Authentication, Access Control, and Single Sign-On
Open Source Web Single Sign-On
Single Sign On module for Apache and NGiNX
LDAP backend for VirtualBox RDP Auth
Deprecated project - see http://wordpress.org/extend/plugins/wpmuldap/