Happy New Year all!

It seems the 'If-Modified-Since' header does not get passed to the back end even when 'proxy_pass_request_headers' is left which should be a default 'on'.

Is there a way to ensure that the 'If-Modified-Since' header is passed?

I have looked at 'proxy_pass_header If-Modified-Since' but I suppose that directive along with 'proxy_hide_header' only manages how Nginx deals with the response headers from the back end to the client while I am trying to deal with the request headers from the client to the back end.

The reason why is that I have a php script that checks this header and responds accordingly but now it always serves a fresh resource rather than a 304 header.

Thanks for your help.