H1514 Shopify API ruby SDK session setup lacks input validation, resulting in SSRF and leakage of client secret

The [Shopify API ruby SDK](https://github.com/shopify/shopify_api) has the ability for the developer to interact with their shop's REST API. When setting up the gem, a code structure similar to the one below may be used to set up the connection:

require 'shopify_api'

class SomeController < ApplicationController
  def index
    ShopifyAPI::Session.setup secret: '<secret>'

    session = ShopifyAPI::Session.new('some-shop.myshopify.com')

    access_token = session.request_token(params)
  end
end