What is the purpose of this directive in the nginx forward proxy example?

[sevmonster]

I have been streamlining my nginx config, and noticed that in the official forward proxy example add_header is used to send a cookie from the auth_request back to the client. However, I do not see this utilized as far as my testing has gone with single application forward proxying. Is this used in domain-level forward proxying? When returning to the app subdomain from the authentik subdomain maybe, to make sure the right cookie is being set? Since in single application forward proxy configuration, the cookie is set by the outpost in its location block under the application subdomain, and in domain-level, you could be on a completely different TLD?

The main reason I am even questioning this is to see if I can remove it from my configuration. I replaced add_header in the example with Headers More's more_set_headers, as I can't use add_header in such a place right now due to nginx config array inheritance. However it appears that more_set_headers overwrites any upstream Set-Cookie headers, whereas add_header leaves them alone. I don't use domain-level proxying, so if that's the only case this cookie header is normally sent, I can safely remove it from my config to let my proxied cookies through.