Without being sure what you mean by "restore user password", here are some things you can do:
In your server side modules, there is a Server class and an Account class.
With these two methods you can do pretty much whatever you want with passwords.
(Note that, shockingly, passwords are stored in clear text.)
server.changeAccountPassword(AccountName, currentPassword, newPassword)
account.getPassword()
If you just want to "recover" an existing password, use account.getPassword and return it to the user.
Or you can just write a new one by first retrieving the old one, and then changing it to something else.
These should work no matter what your data store is, default or otherwise.
Note: for retrieving passwords, my code looks like this:
var account = server.getAccount(name);
pw = account.getPassword();
account.dispose();
There is some warning about account instances that says you have to do that, but I don't remember the details.