I've read in many forums and discussion boards that everyone is having trouble reading/writing data for anonymous users in SharePoint Online public facing sites. Today I noticed that Microsoft has and app called "Contact Us Form" (See below) which does read/write to a SharePoint Online list.
https://sharepointsource123-public.sharepoint.com/_layouts/15/storefront.aspx?source=https%3A%2F%2Fsharepointsource123-public%2Esharepoint%2Ecom%2F_layouts%2F15%2Fviewlsts%2Easpx&sname=SP%20Helper#vw=AppDetailsView,app=WA104092356,clg=0,bm=US,cm=EN%2DUS
So, it looks like Microsoft are the only ones that have been able accomplish this functionality. Are they sharing the secret? Has anyone figured out how they did it. I've tried to look at the .js files, but I'm thinking a bit of C# might have been used because it looks like this app is a "provider-hosted" app. Thoughts?