Encrypting a cookie with HTTP::cookie encrypt and encrypting with an HTTP Profile

Well, at the very least I'd never send the user's password in a cookie, encrypted or not. Otherwise you already have the access session cookie so you could store the password (encrypted) in the session table. Or you could generate a random GUID, make an LTM session table entry with the password, tied to this GUID, and then send that value as a temporary cookie. And if it's a different URL, make that cookie domain-scoped and short-lived.