Dashboard cookies
The dashboard uses a single cookie — the session identifier. Signing in is impossible without it: the browser would have no way to tell the server that the request comes from an already authenticated user.
It contains nothing but a random identifier. No email address, no password and no information about the user is stored inside it — all of that lives on the server and is linked to the identifier.
The cookie is marked as secure-only and inaccessible to page scripts. Its scope is limited to the dashboard address.
It lives until the browser is closed, or for up to thirty days if "remember me" was explicitly chosen. Signing out deletes it immediately, on the server side as well.