How to install and use the Ruby on Rails metal generator?

I am using Ruby on Rails 3 and I am trying start using Rails Metal.

Typing the following in the Terminal

rails generate metal authentication

I get this:

Could not find generator metal.

S开发者_JAVA技巧o, how can I install the metal generator (like a plugin, gem or other)? Where I can find that?

Metal was removed in Rails 3. Here's the commit w/some notes about it:

https://github.com/rails/rails/commit/ed34652d1aca148fea61c5309c1bd5ff3a55abfa