title: How to check session in Shopify
body: <p>How do I check the session for a user which is logged-in?</p>
  
  <p>Once a user has logged in Shopify redirects on <code>my-shop.myshopify.com/account?sid=</code>. Maybe I should check <code>sid</code>? But how can I achieve this?</p>
  
  <p>I also found <code>session ID</code> in cache  - but I didn't find anything helpful in the API.</p>
  
  <p>Such verification is necessary for the <code>customer</code> (not Shopify user/admin).</p>