SameParty cookie attribute

While Google has made strides to remove cookies, there was a recent addition to the Chromium product upon which Chrome, Safari, and Edge are based.

I saw this written up as the following:

The SameParty attribute takes no value, and requires that the cookie also specify the “Secure” attribute, and not specify “SameSite=Strict”. If either of these constraints is violated, the cookie will be considered invalid, and will not be set. “SameSite=Strict” is not supported because “SameSite=Strict” is intended as a security boundary, rather than a privacy boundary (which First-Party Sets aims to establish). Valid use-cases of “SameSite=Strict” in cross-site contexts should not be loosened even when the sites are same-party.

Better stated…

  • The SameParty attribute is specified without a value (as are Secure and HttpOnly) as ;SameParty;
  • The Secure attribute is required in order to use the SameParty attribute. Any cookie specifying SameParty without Secure will be rejected as invalid.
  • Additionally, any cookie specifying SameParty in the presence of SameSite=Strict will be rejected as invalid.

While I’ve seen this implemented in versions of Chrome 89+, it is not yet adopted in Firefox (and may never be).


Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.