caching using ETags to vary the content

[Miles]

Hi

I am using varnish 2.0-beta-2.

I am using varnish to cache a website where there is a small amount of 
personalised content in a particular directory.  When the user is 
outside of that directory, the only difference for logged-in and 
non-logged-in users is a few links (e.g. login/register or view 
profile/logout - the targets are the same irrespective of which user). 
I am trying to come up with a cache setup to deal with this.

How I had planned to deal with this was as follows:
  - set an ETag (e.g. "logged-in" or "anon") depending on whether the 
user is logged in or not;
  - add a "Vary: ETag" header, so varnish stores several representations
  - in varnish, set an "ETag" header on the request when it is received, 
depending on if the user is authenticated or not (can be determined by 
the presence of a cookie).  the request should then match the correct 
page in the cache.

I know varnish doesn't do If-None-Match, but I don't think that is a 
problem in this scheme.

I haven't attempted this yet - can anyone see any holes in it as a 
method?  Or does anyone else have a way of dealing with this sort of 
personalisation-lite?!

Thanks in advance for your help!

Miles