The Authen::PAAS distribution provides a Perl API for authenticating and
authorizing users of computing services. Its design is inspired by
existing pluggable authentication services such as PAM and Java's JAAS, so
people familiar with those two services should be comfortable with the
concepts in Authen::PAAS. At its heart, Authen::PAAS provides a login
service, with pluggable modules for performing different authentication
schemes. The pluggable framework enables the system administrator, rather
than the application developer to define what method is used to
authentication with a particular application.

One might ask, why not just use PAM directly via the existing Authen::PAM
Perl bindings. While this works well for applications which wish to
authenticate against real UNIX user accounts (eg FTP, Telnet, SSH), it is
not particularly well suited to applications with 'virtualized' user
accounts. For example, a web application may maintain a set of virtual
user accounts in a database, or a chat server, may maintain a set of user
accounts in a text configuration file. Since it merely delegates through
to the underlying C libraries, the Authen::PAM module does not provide a
convenient means to write new authentication schemes in Perl. Thus the
Authen::PAAS distribution provides a pure Perl API for authentication.