title: GET a coupon code via URL and apply it in WooCommerce Checkout page
body: <p>I have a WooCommerce website and when customer add-to-cart a product, it is get redirected to checkout page, so cart page is not accessible.</p>
  
  <p>I would like to apply coupon via URL (<code>GET</code>) on checkout page, with something like <code>https://example.com/?coupon_code=highfive</code>.</p>
  
  <p>When customer click this URL then the coupon code is stored in browser sessions. Then if he add-to-cart any product then the coupon is applied into checkout page.</p>
  
  <p>Is this possible?</p>