Replace If-Modified-Since with If-None-Match and If-Unmodified-Since with If-Match.
Pass timestamps instead of date objects between the storage and protocol layer, and remove Last-Modified from responses.
Replace 304 and 409 with 412.
Use 201 for PUT requests that create an item.
Include the auth endpoint in WebFinger response indexed by the OAuth version URI. Keep the auth-method and auth-endpoint properties for backward compatibility.