Cookie transparency

It would be nice to be able to partially disable the session cookie in Rails.

I have a public facing website, where I would like to avoid using cookies.

Except: On certain urls, like /admin/*, where session cookies are necessary for login.

if flash has been set, the cookies are necessary for any url, but should be readable. Not hidden behind a session cookie id.

I just want to avoid cookies, that look like tracking cookies, ie the Rails session cookie.