Adding ArcGIS for Server secured services in a web map fails with errors

Description

In Internet Explorer 9 or earlier, after switching the server to HTTP and HTTPS, users are unable to access layers of a web application hosted on ArcGIS Online containing services from ArcGIS for Server.

Opening individual services via the REST endpoint also fails. When attempting to add ArcGIS for Server secured services in an ArcGIS Online web map and login credentials are entered, the following error is returned: "Unable to access the authentication service."

Cause

This is a known issue. The services are secured with GIS-tier authentication, where users are authenticated using Esri's proprietary ArcGIS token-based authentication mechanism. The request to generate a token in the ArcGIS Online map viewer goes through the ArcGIS Online sharing proxy. The sharing proxy for ArcGIS Online (for example, http://ess.maps.arcgis.com/sharing/proxy) returns a "502 Bad Gateway" error in some cases when attempting to generate a token against an ArcGIS for Server token service if an alias is used for the server. Hence, when a REST service layer is added to ArcGIS Online, the following error displays: "Unable to access the authentication service."

Note:
The error, "Unable to access the authentication service", may also occur because of due to an expired Secure Sockets Layer (SSL) certificate. For more information, please refer to the Esri Knowledge Base article, Error: Unable to access the authentication service. 

Solution or Workaround

Note:
By default, the error does not occur in Mozilla Firefox or Google Chrome because these browsers allow the application to make the requests, whereas settings in Internet Explorer must be updated.