The old version assumed `json_decode` would return an associative array.
While it can do so if an extra option is specified, the default
behaviour is to return an object. Therefore, a successful password
change resulted in an error while parsing the response.
The new code is accessing the response as object instead. The method
is now covered by a unit test.
This driver does not use an admin account. It uses the user's account to
authenticate at the Webmail API. It uses the recommended UAPI and does
not rely on third-party classes.
