After enabling either Basic or Windows Authentication of a Geospatial Portal (applies also to Webmap Publisher Portal) instance via IIS the Portal is accessible via HTTPS, however it is not configurable via the Admin Console which responds with general error 'Exception Occurred'.
This error is caused by the Authentication Setting on both the Admin Console and Portal Instance 'AdminService' virtual directory, which controls configuration.
To resolve ensure that 'Anonymous Authentication' is enabled in IIS on the AdminService virtual directories for both:
1. The WebMap Publisher Portal or Geospatial Portal instance you are trying to configure
2. The Admin Portal instance
After applying these changes be sure to restart IIS services.