WebDAV engine passes structure to this method by reference.
All fields of the structure are provided by WebDAV client except field.
In your Lock implementation you must create lock token and set member.
You must also associate generated token with the hierarchy item in the repository during this call.
The token is sent to the WebDAV client.
public Task LockAsync(LockLevel level, bool isDeep, TimeSpan? requestedTimeOut, string owner)