Get rid of Class variable storage and move to instance storage

I'm building an admin/monitoring server that handles requests from both out production and qa Shopify store.
In the current setup, the user/password/site_uri are stored at the class level, so I can't create a prod session and a qa session and store them in memory.
For every request to the REST server I have to clear the current class variables and set for requested environment.

Additionally, this is not thread safe. If two REST requests arrive at the same time for different endpoints, they will clobber each other.

先追蹤 user、password 和 site_uri 儲存在哪裡，以及 REST 請求如何存取它們，接著檢視如何為不同的 Shopify 環境建立和選取 session。完成的標準是 production 和 QA session 可以在記憶體中共存，且並行請求不再互相覆寫設定；為這兩種情況新增或執行 coverage。