Shopify API: Get url that leads directly to checkout

What options are there to forward people directly to a checkout page for a specific product in a Shopify store?

This is interesting for me for the following scenario:

1. User goes on my website where I talk about a product
2. Clicks a-href button
3. Gets directed to the checkout page (not product page) on my Shopify store

I have read the Product-sections on the API documentation but couldn't find a hint.