The Dropbox plugin can be used to access a dropbox account via API. To use it, you must first register as Dropbox developer to get your API Key.
This is typically a driver with wich you create a Repository Template, leaving the users credential empty and filling only your API Key info : that way, the users are able to access their own DropBox account without the administrator having to know their credentials, but using a shared API Key. See the documentation about the Repository Templates.
In Pydio v6, Pear::Http_OAuth package was required. It is not anymore in v7 and following.