Get access token via facebook oauth. API key and API secret are saved with Config::Pit.

AccessToken.rb

# -*- coding: utf-8 -*-
require 'rubygems'
require 'net/https'
require 'pit'

OAUTH_DOMAIN       = 'graph.facebook.com'            # ホスト名
OAUTH_PATH         = '/oauth/access_token'           # パス
OAUTH_QUERY_APIKEY = 'client_id'                     # API Keyのクエリパラメータ
OAUTH_QUERY_APISEC = 'client_secret'                 # API secret のクエリパラメータ
OAUTH_QUERY_TYPE   = 'grant_type=client_credentials' # 固定

config = Pit.get("wt_test", :require => {
    "api_key"    => "Your App ID / API Key",
    "api_secret" => "App Secret"
})

https = Net::HTTP.new(OAUTH_DOMAIN, 443)
https.use_ssl = true;
https.verify_mode = OpenSSL::SSL::VERIFY_NONE        # 安全ではない？
result = https.get(OAUTH_PATH + '?' +
      OAUTH_QUERY_APIKEY + '=' + config['api_key'].to_s + '&' +
      OAUTH_QUERY_APISEC + '=' + config['api_secret'].to_s + '&' +
      OAUTH_QUERY_TYPE)

puts result