[websec] Question regarding RFC 6797

[Claudio Saavedra <[e-mail]>]

Hi,

I am currently implementing HSTS support for libsoup and there is one
point that I find confusing and I would appreciate your comments. 

Section 8.1 states:

   Update the UA's cached information for the Known HSTS Host if either
   or both of the max-age and includeSubDomains header field value
   tokens are conveying information different than that already
   maintained by the UA.

The way I understand this is that if a HSTS host keeps sending the same
values to a conforming client, this should not update the information
cached and hence the cached information will expire after max-age
seconds have passed since the _first_reception_ of this header.

However, section 11.2 states:

   The "constant value into the future" approach can be accomplished by
   constantly sending the same max-age value to UAs.

   For example, a max-age value of 7776000 seconds is 90 days:

   Strict-Transport-Security: max-age=7776000

   Note that each receipt of this header by a UA will require the UA to
   update its notion of when it must delete its knowledge of this Known
   HSTS Host.

This seems to contradict what I quoted from section 8.1. If the server
constantly sends a max-age of 7776000 and includeSubDomains is not
changed (which is implicit in the example), then by 8.1 the cache
information won't be updated.

Would you mind clarifying this?

Best regards,

Claudio