HTTP Vary Header

About

The Vary 1) HTTP response header specifies header values that should be added to the cache key used by the cache.

Usage

Not mixing content for mobile vs desktop

A server may serve different contents for desktop or mobile depending on the user-agent header.

If the cache uses only the URL has cache key, a desktop page could be served to a mobile page.

To avoid this situation, you can add the user-agent header in the Vary header to instruct caching servers to add the user agent header to the cache key. 

Vary: User-Agent

Security

If you don't want to serve the same page to different users. 

Vary: Cookie

Set

The Vary header value should be the same:

1)
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Vary




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