Stripe Return url - How to get & specify the current page URL?

I am trying to use the below API call to open customer portal in Stripe

curl https://api.stripe.com/v1/billing_portal/sessions \
  -u "stripe_api_key" \
  -d customer={{CUSTOMER_ID}} \
  --data-urlencode return_url="https://example.com/account"

https://docs.stripe.com/customer-management/integrate-customer-portal?lang=curl#configure

My question is related to the return_url. I want the user to be able to return to the same page he was when he clicked on the Open Portal Button . How do i populate the return_url with the current page URL?