I have a web app that I would like to share with individuals from outside of my organization. The other organization only has a public account (no subscription to ArcGIS online). Is it possible to add their usernames to a group that I have created so that I can share specific content with them? If this is not possible, what options do I have to share the web app with their organization? I read something about a "viewer" type user, but I do not know if I have the ability to set one up. The information is sensitive, so I cannot share it publicly.