Yet another potentially breaking change on the web. This time round it involves cookie handling (in the upcoming Chrome 80). The objective is to close off a class of attacks known as CSRF (cross-site request forgery). Expect other browsers to follow suit.
… any websites you’re responsible for that are passing cookies around cross domain by POST request and don’t already have a SameSite policy are going to start misbehaving pretty quickly
Source: Troy Hunt: Promiscuous Cookies and Their Impending Death via the SameSite Policy