What is a safe way of knowing the referer/referrer in an HTTP request? <p>I am using nodejs to write an image upload service. Paying clients will be able to send an image file to my endpoint that I have set up on my server. However, when every request comes in, I need to confirm that it is actually a paying client making the request. I thought about having the client give me their domain name and I would just check the referer header. However, someone could easily spoof the referer header and use my service without paying. How do SaaS developers face this technical problem? Is it possible to fix this without requiring my clients to have some server side code?</p>