module Roda::RodaPlugins::ConditionalSessions

def self.load_dependencies(app, opts=OPTS, &block)

a request method for whether sessions are allowed.
Pass all options to the sessions block, and use the block to define 
def self.load_dependencies(app, opts=OPTS, &block)
  app.plugin :sessions, opts
  app::RodaRequest.class_eval do
    define_method(:use_sessions?, &block)
    alias use_sessions? use_sessions?
  end
end