Cookies are typically sent to third parties in cross origin requests. This can be abused to do CSRF attacks. Recently a new cookie attribute named SameSite was proposed to disable third-party usage for some cookies, to prevent CSRF attacks.
Same-site cookies allow servers to mitigate the risk of CSRF and information leakage attacks by asserting that a particular cookie should only be sent with requests initiated from the same registrable domain.
The server can set a same-site cookie by adding the SameSite=... attribute to the Set-Cookie header:
Set-Cookie: key=value; SameSite=strict
There are two possible values for the same-site attribute:
In the strict mode, the cookie is not sent with any cross-site usage even if the user follows a link to another website. Lax cookies are only sent with a top-level get request.