gem 'simple_wechat'

client = SimpleWechat::Client.new("APPID", "APPSECRET")
access_token = client.get_access_token  
# access_token and expires_in are wrapped in access_token.

jsapi = SimpleWechat::JsApi.new
ticket = jsapi.get_ticket("ACCESS_TOKEN")
# ticket, errcode, errmsg, expires_in are wrapped in ticket.

ticket = "sM4AOVdWfPE4DxkXGEs8VMCPGGVi4C3VM0P37wVUCFvkVAy_90u5h9nbSlYy3-Sl-HhTdfl2fzFy1AOcHKP7qg"
jsapi = SimpleWechat::JsApi.new
config = jsapi.get_config(ticket, "http://wx.qq.com", "APPID", ["previewImage"])
# now MultiJson.encode(config) can be passed into function wx.config() in javascript.

class SessionsController < ApplicationController
  def auth
    redirect_to auth_client.authorize_url(REDIRECT_URL, state)
  end

  def callback
    if state == params[:state]
      access_token = auth_client.get_token(params[:code])
      # do something with access_token. 
      # for example, call access_token.openid to get openid
    end
  end

  private

  def auth_client
    @auth_client ||= SimpleWechat::Client.new(APP_ID, APP_SECRET).get_auth_client
  end
  
  def state
    session[:state] ||= SecureRandom.hex(3)
  end
end