How to redirect without changing URL?

Question

PHP

How can I redirect from one domain to another without changing the URL?
You need to set up a redirect from the addresses:
https://u.domain.com/(.*)
to
https://apitest.domain.com/u/$1
so that the URL in the address bar does not change.

Answer 1

iframe?

Answer 2

Something like this:

if ($host ~* ^u.domain.com\.(.*)$) {
  rewrite / https://apitest.domain.com/u/$request_uri permanent;
}

Answer 3

You need to do a 302 redirect (temporary).
The browser will load another URL while leaving the old one displayed.
True, it is possible that this will not work cross-domain.