This attribute has shipped with chrome 51, seems like a nice thing for statehood and hapi to support as well.

https://tools.ietf.org/html/draft-west-first-party-cookies-07#page-3

Set-Cookie: SID=31d4d96e407aad42; SameSite=Strict

Possible values are None, Strict, and Lax https://tools.ietf.org/html/draft-west-first-party-cookies-07#section-4.1.1