I'm surprised I couldn't find any answers.
How do I set my sessionid in my cookie to expire at the end of session? (when the browser closes or the user has been inactive for a period of time).
The two solutions I found were
(httpcookie).Expires = HttpContext.Current.Session.Timeout
Which gave me a compile error so I don't know if the user checked his code before posting. And the other was to set the expire date to 1 day ago which my gut says is wrong. How do I do this?