Add support for "default" value for "sameSite" cookie attribute

[lutien]

To align with the changes introduced for WebDriver BiDi in this pr we should also introduce the value "default" in WebDriver Classic.

[lutien]

I did some preparatory research of current behavior among the vendors: https://bugzilla.mozilla.org/show_bug.cgi?id=1975767#c3.

[css-meeting-bot]

The Browser Testing and Tools Working Group just discussed Add support for "default" value for "sameSite" cookie attribute in WebDriver Classic.

The full IRC log of that discussion

<jgraham> Topic: Add support for "default" value for "sameSite" cookie attribute in WebDriver Classic
<jgraham> github: Add support for "default" value for "sameSite" cookie attribute in WebDriver Classic
<jgraham> github: https://github.com//issues/1908
<tidoust> sasha: We add the "default" value for "sameSite" cookie in BiDi because we had a situation where you could read cookies through document.cookie but not set them with the cookie API.
<tidoust> ... The question is whether we should do the same for Classic as well. The main question for me here is Classic is even more vague about cookies. Lax and Strict. But it also says that sameSite should be no.
<tidoust> ... I think Chrome for Classic works in this case. Maybe it would be acceptable to let browsers return values that work for them.
<jimevans> q+
<tidoust> ... Is it OK to introduce a change? Would it break something, for example for Selenium?
<jgraham> ack next
<tidoust> jimevans: That's not going to cause anything breaking from a Selenium perspective.
<jgraham> q+
<tidoust> ... We're still working on how to translate our cookie handling code in Selenium to use BiDi. Any change we make here, we can adapt to.
<jgraham> ack next
<tidoust> jgraham: In general, cookies have changed a lot recently and the Classic spec has not... It was written when cookies were slightly simpler. We didn't have the complexity that BiDi deals with now.
<jimevans> q+
<tidoust> ... How much time do we want to spend fixing that vs. getting people to move to BiDi is a good question.
<jgraham> ack jimevans
<tidoust> jimevans: I don't think that it's going to adversly affect Selenium even if we update the Classic spec. If spec and browser implementations change, then Selenium code will change to it.
<jgraham> RRSAgent: make minutes
<tidoust> ... So no objection to changing Classic here.
<RRSAgent> I have made the request to generate https://www.w3.org/2025/07/09-webdriver-minutes.html jgraham
<sasha> q+
<jgraham> ack next
<tidoust> ... Same question about how much time to spend on Classic vs. BiDi.
<tidoust> sasha: Maybe the way it works now is acceptable. You cannot set anymore the cookies with sameSite ... There will be no error, but the cookie cannot be set.
<tidoust> ... If it's an acceptable behavior for clients, that's fine.
<tidoust> jgraham: It the current situation leads to data loss, that may be a good motivation to fix things.