/usr/share/perl5/Plack/ is in libplack-middleware-session-perl 0.21-1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/perl5/Plack/Middleware/
/usr/share/perl5/Plack/Middleware/Session/
/usr/share/perl5/Plack/Middleware/Session.pm
/usr/share/perl5/Plack/Middleware/Session/Cookie.pm
/usr/share/perl5/Plack/Session/
/usr/share/perl5/Plack/Session.pm
/usr/share/perl5/Plack/Session/State/
/usr/share/perl5/Plack/Session/State.pm
/usr/share/perl5/Plack/Session/State/Cookie.pm
/usr/share/perl5/Plack/Session/Store/
/usr/share/perl5/Plack/Session/Store.pm
/usr/share/perl5/Plack/Session/Store/Cache.pm
/usr/share/perl5/Plack/Session/Store/DBI.pm
/usr/share/perl5/Plack/Session/Store/File.pm
/usr/share/perl5/Plack/Session/Store/Null.pm