How to store an object in a cookie?

Question

While this is possible in C#: (User is a L2S class in this instance)

User user = // function to get user
Session["User"] = user;

why this is not possible?

User user = // function to get user
HttpCookie cookie = new HttpCookie();
cookie.Value = user; 

and how can it be done? I don't want to store the id of the user within the cookie and then do some validation.

Btw, if possible, is it secure to store an object within a cookie rather than only the ID ?

Answer 1

A cookie is just string data; the only way to do that would be to serialize it as a string (xml, json, base-64 of arbitrary binary, whatever), however, you shouldn't really trust anything in a cookie if it relates to security information ("who am I?") as a: it is easy for the end-user to change it, and b: you don't want the overhead of anything biggish on every single request.

IMO, caching this as the server is the correct thing; don't put this in a cookie.