How to get the redirect source in PHP?

How to get the redirect source in PHP?
For example, www.a.com redirects to www.b.com through header location. How does www.b.com obtain the redirection source to determine whether this visit is redirected from www.a.com?

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How to get the redirect source in PHP?
For example, www.a.com redirects to www.b.com through header location. How does www.b.com obtain the redirection source to determine whether this visit is redirected from www.a.com?

Can php get referer from header?

js has this referer, which is the access source. The author can search it on Baidu, and then you can use this

Try to get it via $_SERVER['HTTP_REFERER']

The answer is that it cannot be obtained.