An authentication provider for Dancer::Plugin::Auth::Extensible which
authenticates Linux/Unix system accounts.
Uses Unix::Passwd::File to read user details, and Authen::Simple::PAM to
perform authentication via PAM.
The get_user_details call for this provider will return information from the
passwd file - expect gecos, gid, uid, home, shell, uid.
Unix group membership is used as a reasonable facsimile for roles - this seems