Unable to access federated ArcGIS Servers

Description

Attempts to access federated ArcGIS Servers fail, and the following error message is returned:

Error:   
Error code 403. Access to this resource is not allowed. Access to this resource is forbidden.

In some cases, running the analysis tools from Portal for ArcGIS Map Viewer Classic fails, and the following error message is returned:

Error:   
Unable to access the analysis service.

Cause

The errors occur if the server URL is configured incorrectly when federating ArcGIS Server with Portal for ArcGIS. For example, in the case below, a slash (/) is added after 'arcgis' in the URL, which is incorrect.

https://machine.domain.com/arcgis/

The default URL configuration is:

https://machine.domain.com/arcgis

Solution or Workaround

1. Log in to the ArcGIS Server Administrator Directory with an administrator account, and click security.

2. In the ArcGIS Server Administrative Directory window, under Security, click config.

3. On the Security Configuration page, navigate to the bottom page and click update.

4. On the Update Security Configuration page, navigate to Portal properties under the Configuration Properties section.
5. Search for the serverUrl property, and edit the URL to follow the format described below.

https://machine.domain.com/arcgis

Note:
Ensure there are no additional slashes at the end of the URL.

6. Click Update.