This function deals with the Webfinger lookup, discovering a connecting user’s storage details.
The discovery timeout can be configured via `RemoteStorage.config.discoveryTimeout` (in ms).
| userAddress | user@host |
A promise for an object with the following properties.
| href | Storage base URL, |
| storageType | Storage type, |
| authUrl | OAuth URL, |
| properties | Webfinger link properties |