Login the user on the session prompting for passwords interactively when necessary.
This call will return immediately and completes asynchronously.
| this |
session to use for login |
| user_type |
the type of login user |
| interaction |
interaction to request PIN when necessary |
| cancellable |
optional cancellation object, or null |
| callback |
called when the operation completes |
| user_data |
data to pass to the callback |