alias_method_chain and Class methods (a Ruby question)

Hello list,

I am trying to override the post_form method of Net::HTTP so that it does something before actually doing the post. I tried the following in environments/development.rb

   module Net
     class HTTP

     alias_method_chain :post_form, :intercept

     def post_form_with_intercept(url, params)
       # Do something before post
       logger.info('About to post at #{url}')
       post_form_without_intercept(url, params)
     end
   end

Unfortunately this complains that there in no method called post_form:

  ... :NameError: undefined method `post_form' for class `Rails::Initializer::Net::HTTP'

I also tried opening the Net module with:

   module ::Net

but then I get:

  ... :NameError: undefined method `post_form' for class `Net::HTTP'

Any ideas how I can achieve what I want?

-christos