How To Install and Configure PAM OpenOTP Plugin to Enable Multifactor Authentication on Linux Machines Simple login flow Push Login flow 1. Background On Unix-like systems, processes such as the OpenSSH daemon need to authenticate the user and learn a few things about him or her (user ID, home directory, …). Authentication is done through a mechanism called Pluggable Authentication Modules, and retrieving information about users (or even groups, hostnames, …) is done through another mechanism, called the Name Service Switch.