** Using WeBWorK **

The "r" key of the $self object no longer exists.  That was the modPerl Apache::Request object.  WeBWorK 2.18 and 2.19 do not use modPerl anymore.  Now there is a Mojolicious::Controller object.  You can access that in the "c" key of the $self object.  So use $self->{c} instead.  The Mojolicious::Controller object has a "param" method that works the same as before.  So the rest of your code should work.