HTTPS, short for Hypertext Transfer Protocol for Secure communication, allows for the secure transmission of data, both incoming and outgoing, between a client, such as a web browser, and the server. Esri is making the HTTPS-Only change in a phased approach. Esri customers must act now to be ready for this change.
Currently, ArcGIS Online supports configuring HTTP or HTTPS. With the update planned for December 8, 2020, the “HTTPS Only” default will be enforced, and customers will no longer have the option of turning it off. However, for ArcGIS Enterprise the customer has full control of the HTTPS/HSTS enforcement for their configuration.