[Questions] How to use Parse Server to allow anonymous user groups #1843

I'm building an app that allows users to upload/view/download and interact with the images others have uploaded to the group. The app doesn't require register/log in at all. In order to join a group, the user only need to enter a string key which is distributed by the creator of each group.

I am really stuck right now as in how do I achieve this? I looked into Parse Server + Heroku, Firebase + App Engine, and AWS Mobile Hub, but I have no idea how to implement such features on each of these services. All help / suggestion are appreciated! :)