Hi

It was my review that triggered this, so I'd like to explain my position.

There are several things that could be considered failures of the TLS layer:
 1. Revoked certificate
 2. No CRL/OCSP response
 3. Expired certificate
 4. Expired CRL (yes, I know NextUpdate is not expiry…)
 5. Mismatch between hostname and certificate (CN or alt name)
 6. Some other things I forgot?

I believe we all agree that #1 should be a hard fail. Maybe even in the absence 
of HSTS. #2 is usually not treated as a failure today - it doesn't trigger a 
warning screen in any browser. I haven't tested this with HSTS, but I'd be 
surprised if this causes a hard fail. Same for #4.

AFAIK the most common failure cases are #3 and #5. Certificates do expire, and 
even some well-run, security conscious site administrators have been known to 
let them expire. 
Mismatching domain names is an issue, because two FQDNs might point to the same 
server. IMO this is a good argument for a report-only setting, whereas the 
expiry is something that will bite you far after your supposedly successful 
deployment.

I guess my issue with this is because when I read the draft for the first time, 
I thought this would be a good idea for websites that only do HTTPS and do not 
do HTTP except to redirect to HTTPS. I thought it would allow them to signal 
this information, and allow them to defeat HTTP-based MiTM attacks. The draft 
as it stands is not a good fit for this use case, because it requires more of 
the administrator than is currently reasonable to expect.

I could propose an "HSTS-light" header for this use case, but I don't think 
anybody would like to have that. 

Yoav
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