But what if one website wanted user data from another website. Couldn't b.com make a GET request to a.com(assuming the user is on b.com now, and was on a.com pr

But what if one website wanted user data from another website. Couldn't b.com make a GET request to a.com(assuming the user is on b.com now, and was on a.com previously, with a cookie), using the cookie for a.com in the browser and get the user's info from a.com, then send that to b.com? All without the user or a.com knowing?