I think it would be a good idea if there was a username and a password variable that you could use to reference what you have already entered in for the username and password. For example, $USERNAME for username and $PASSWORD for password. The reason for this, I find that some websites require me to make a custom field and re-enter my password or username so that it will auto fill correctly. When I do that, but say have to change my password, I then have to go in and update the custom field as well with the new password/username.
Let me know what everyone thinks or if I need to clarify.