To align with the latest specification in RFC 6265bis, Chromium will reject cookies with a "Domain" attribute that contains a non-ASCII character (e.g. Domain=éxample.com).
Support for IDN domain attributes in cookies has been long unspecified, with Chromium, Safari and Firefox all behaving differently. https://github.com/httpwg/http-extensions/issues/1707 fixes this issue by standardizing Firefox's behavior of rejecting cookies with non-ASCII domain attributes. Since Chromium has previously accepted non-ASCII characters and tried to convert them to normalized punycode for storage, we will now apply stricter rules and require valid ASCII (punycode if applicable) domain attributes.