How to implement a referral link?

Question

Python

For example, I take any site, add a referral policy (in the head), but (on the site) document.referrer still returns an empty string and the title (in the body of the head tag) is not added ... Please help.

head = {'Referrer-Policy': 'no-referrer-when-downgrade'}
r = requests.post("https://httpbin.org/post", headers = head)
print(r.text)