Vary Header

Declares which request fields influenced the selected response representation.

Use Vary when content or CORS responses differ based on request headers so caches do not serve one variant to another request.

httpcachecorsheader

Reference (http)

Vary: Accept-Encoding, Origin

Use Vary when content or CORS responses differ based on request headers so caches do not serve one variant to another request.

Common mistakes

Omitting Vary: Origin when Access-Control-Allow-Origin changes by requesting origin.

IANA registry: http-fields/field-names

Sources