How to prompt user for credentials?

`manage.js` has
```js
const user = firebase.auth().currentUser;

// TODO(you): prompt the user to re-provide their sign-in credentials
const credential = promptForCredentials();

user.reauthenticateWithCredential(credential).then(() => {
// User re-authenticated.
}).catch((error) => {
// An error ocurred
// ...
});
```

But what does it mean by prompt the user to re-provide credentials? Does it mean their email and password or...?

Read the reauthentication example in manage.js and trace how promptForCredentials is described or used. Clarify what credentials the snippet expects and what a user should provide, then verify that the updated explanation matches the reauthenticateWithCredential flow.

Written by the indexing model from the issue text.