twitter_reverse_auth_controller.rb

class TwitterReverseAuthController < ApplicationController
  def api_key_exchange
    user_credentials = UserCredentials.new(params.slice(:screen_name, :token, :secret))
    if user_credentials.valid?
      user  = user_credentials.user
      token = params[:token]
      device = Device.find_or_create_by_token!(params.slice(:token, :description).merge(:user_id => @user.id))
      render :json => { :api_key => device.api_key }
    else
      render :json => { :error => user_credentials.first_error}, :status => :unprocessable_entity }
    end
  end
end

class UserCredentials
  def initialize(screen_name, token, secret)
    # ...
  end

  def valid?
    # ...
  end

  def first_error
    # ...
  end
end