Calls to document.cookie continue to work as they have before. You can provide
the SameSite attribute as part of the assigned string.
// Set a same-site cookie for first-party contexts
document.cookie = 'cookie1=value1; SameSite=Lax';
// Set a cross-site cookie for third-party contexts
document.cookie = 'cookie2=value2; SameSite=None; Secure';