[hint] HTTP Protocol header compliance

[Malvoz]

Moving towards HTTP/2, and eventually HTTP/3 it'd be helpful if we could have a hint for incompatible, obsolete or deprecated headers.

For example, according to this wikipedia article, the following header fields must not be used with HTTP/2:

• Connection
• Proxy-Connection
• TE (unless trailers value is present).
• Transfer-Encoding
• Upgrade
• Upgrade-Insecure-Requests

This check should also disallow the same non-compliant headers within the Vary (https://github.com/webhintio/rfcs/issues/34) header field if applicable.

[molant]

This is a good idea! So if I've understood you correctly, have a hint that reports obsolete headers depending on the (most recent) protocol used by the site, right?
Should we try to request the site with different protocols (similar to what we do with http-compression or would that be a bit overkill? Maybe an option to do a deeper scan? If so, we will have to figure out how to check what protocol(s) are supported by the site (and figure out how to add support for it in the jsdom connector). @webhintio/contributors thoughts?

[hxlnt]

Additionally, we should consider addressing HTTP header name casing.

Reference: https://twitter.com/jamesmunnelly/status/1145955413248172032?s=21