For login cookies, there are two common methods of storing login information in cookies: a signed cookie or a token cookie.
Signed cookies store the user's name, when they last loggedin, and whatever else the service may find useful. Along with this user-specific information, the cookie also includes a signature that allows the server to verify that the information that the browser send hasn't been altered.
Token cookies use a series of random bytes as the data in the cookie. On the server, the token is used as a key to look up the user who owns that token by querying a database of some kind.
For the visit, we'll update the login HASH for the user and record the current timestamp for the token in the ZSET of recent users. If the user was viewing an item, we also add the item to the user's recently viewed ZSET and trim that ZSET if it grows past 25 items.