Pluggable Authentication Modules (PAM)
Linux uses PAM (pluggable authentication modules) in the authentication process as a layer that communicates between the user and an application. PAM modules are available on a system wide basis, so they can be requested by any application. PAM allows for applications, such as system daemons, to share a single, unified authentication widget. Otherwise, each application would have to include an individually written system which would result in weaker overall security and issues with compatibility. PAM modules, which are a set of shared libraries for a specific authentication mechanism.