a Last.FM Strategy for OmniAuth

lastfm.rb

require 'omniauth/core'
require 'digest/md5'
require 'rest-client'
require 'multi_json'

module OmniAuth
  module Strategies
    class Lastfm
      include OmniAuth::Strategy

      attr_accessor :api_key, :secret_key, :options

      def initialize(app, api_key, secret_key, options = {})
        super(app, :lastfm)
        @api_key    = api_key
        @secret_key = secret_key
        @options    = options
      end

      def request_phase
        params = { :api_key => api_key }
        query_string = params.map{ |key,value| "#{key}=#{Rack::Utils.escape(value)}" }.join('&')
        redirect "http://www.last.fm/api/auth/?#{query_string}"
      end

      def callback_phase
        token = request.params['token']
        params = { :api_key => api_key }
        params[:token] = token
        params[:api_sig] = signature(token)
        params[:method] = "auth.getSession"
        params[:format] = "json"
        response = RestClient.get('http://ws.audioscrobbler.com/2.0/', { :params => params })
        @json = MultiJson.decode(response.to_s)

        extra_params = { :method => "user.getInfo", :user => @json['session']['name'], :api_key => api_key, :format => "json" }
        extra_response = RestClient.get('http://ws.audioscrobbler.com/2.0/', { :params => extra_params })
        @extra_json = MultiJson.decode(extra_response.to_s)
        super
      end

      def user_info
        {
          'name'     => @extra_json['user']['realname'],
          'nickname' => @extra_json['user']['name'],
          'location' => @extra_json['user']['country'],
          'image'    => @extra_json['user']['image'],
          'urls'     => {
            'Profile' => @extra_json['user']['url']
          }
        }
      end

      def auth_hash
        OmniAuth::Utils.deep_merge(super, {
          'uid' => @extra_json['user']['id'],
          'user_info' => user_info,
          'extra' => {
            'user_hash' => @extra_json['user']
          },
          'credentials' => {
            'token' => @json['session']['key']
          }
        })
      end

      protected
        def signature(token)
          sign = "api_key#{api_key}methodauth.getSessiontoken#{token}#{secret_key}"
          Digest::MD5.hexdigest(sign)
        end
    end
  end
end