While HAL can do a lot of things and can remember a good deal from users' conversations, I would not wish to trust HAL with my private Passwords! There is very little in the way of security or trust with HAL and in doing so, you would assume all of the risk.
There are specific Password Managers whose main duty is to collect, encode, and safeguard the user's passwords and other private information.
Hal wasn't designed for that but I'm sure someone could create a plugin that might allow Hal to do that.