Conditional backend requests with beresp.ttl=0.

[Nick]

Hi,

I'm wondering if there is a way to configure varnish to send conditional 
requests to the backend when "Cache-Control: no-cache" has been returned 
in a response with an "Etag".

I've tried setting beresp.ttl = 0s and beresp.keep = 1d, but the keep 
time seems to be ignored and the backend isn't getting an 
"If-None-Match" header.

I'm using Varnish 4.0.3, but I've noticed that setting ttl=0s seems to 
cause the keep time to be ignored.  I think the grace time might also be 
ignored, though I haven't verified that yet.

The only way I've been able to force behaviour similar to what I'm 
looking for is to set ttl=1s, but there is a use case where it isn't 
desirable to wait that extra second.

I've also tried setting max-age=0.

Any help would be appreciated!

-- 
Nick