Add Custom Private Fields/Content

My client likes what I’ve done with the core product. I am not sure if this is the place to post this, so if it’s not please tell me where I should go. I was looking for an add-on that would allow me the ability to create custom fields and make those custom fields private to staff only, i.e., a login would be required to add, edit or view this content. Is there such a plugin/add-on or would this need to be contracted out to a developer to assist me with this?