In ArcGIS Online, adding a layer using the Add Layer from Web option returns the following error:
Error: Unable to add the layer because the organization requires all communication to occur over a secured internet connection (HTTPS)
The ArcGIS Online security setting is disallowing HTTP connections. In ArcGIS Online, the Allow access to the organization through HTTPS only option is enabled by default, which is the cause for the error.
Warning: The following workaround disables HTTPS in ArcGIS Online. Using mixed content can lead to a compromised experience for the user and vulnerabilities for the organization. Consult with a qualified computer systems professional, if necessary. Esri cannot guarantee results from incorrect modifications while following these instructions. Therefore, use caution and proceed at your own risk.