Sunlight API access

implementation

s = Sunlight::UrlGenerator.new("inventory/904655", {format: "json"})

At this test run the URL evaulated to https://services.sunlightsupply.com/v1/inventory/904655?format=json&X-ApiKey=gMgF47gaFdncTcE2GLoTEdmAcXHWakNXyKdPZjKSoiMAWgWLCR&time=2014-05-19T18:59:49Z&signature=113295BAAD176C82CD09127F7CB5E4135B995FA1

I got an invalid signature

sunlight.rb

module Sunlight
  class << self
    def public_key
      "gMgF47gaFdncTcE2GLoTEdmAcXHWakNXyKdPZjKSoiMAWgWLCR"
    end 

    def secret_key
      "8w8HP3T3yF2z3pgyjic6"
    end 
  end 

  class UrlGenerator
    attr_reader :url
    def initialize( uri_suffix, get_params={} )
      @base_url = "https://services.sunlightsupply.com/v1/#{uri_suffix}?"
      @get_params = get_params
      @time_stamp = Time.zone.now.strftime("%Y-%m-%dT%H:%M:%SZ")
      append_get_params
      append_api_key
      append_time_stamp
      append_signature
    end 

    def append_get_params
      @get_params.each_with_index do |(key,value), i|
        @base_url += "#{key}=#{value}"
        @base_url += "&" unless i == (@get_params.size - 1)
      end 
    end 

    def append_api_key
      @base_url += "&" if @get_params.size > 0 
      @base_url += "X-ApiKey=#{Sunlight::public_key}"
    end 

    def append_time_stamp
      @base_url += "&time=#{@time_stamp}"
    end 

    def append_signature
      @signature = Digest::HMAC.hexdigest(@base_url, Sunlight::secret_key, Digest::SHA1).upcase
      @url = "#{@base_url}&signature=#{@signature}"
    end 
  end 

end