As a side note the thing I find most puzzling about RFC 6797 is that the 'max-age' field can be set to 0 to invalidate the HSTS flag for the domain, but can't be set to an indefinite value. The inability to deal with stripping before reception of the 'Strict-Transport-Security' header is understandable, but lack of indefinite retention of the HSTS flag is hard to comprehend.