If you want someone to log into their Shopify account before they can rate your products, simply follow these steps:

• Log into your store’s Management Dashboard and open your Template’s Editor:
  Themes -> Customize theme -> Edit HTML/CSS.
• There, find Snippets/rw-settings-custom.liquid and click it.
• Add the following code:

  {% if customer %}{% else %}
      settings.options.readOnly = true;
  {% endif %}
  

• Now Save the file and you done

If you have no clue about coding or liquid files modification, feel free to contact us. Our Shopify experts would be happy to do it for you for a symbolic setup fee.