I want to use OAuth2 to give authenticated users access to feature layers in my ArcGIS.com portal. I've looked at the OAuth samples and I've been having some difficulty in figuring out how to use it properly. It would be helpful if there was an explanation of what the oauth_callback.html file does and how it works with the index.html, the script shown on the sample page. I was getting errors when trying to register the script in ArcGIS.com and had to call Support, who were stumped for quite a while also. They finally figured out that oauth_callback.html is what you have to register in ArcGIS.com.
By the way, the oauth_callback.html file in the zipped download files for both OAuth samples still contain references to 3.10, even though the live sample and sandbox pages use 3.11