json.decoder.JSONDecoderError:Expecting value: line 1 column 1

Error Message

Running an ArcGIS API for Python script that requires signing in to Portal for ArcGIS may fail and return the following error:

Error:
json.decoder.JSONDecoderError:Expecting value: line 1 column 1

Cause

This error occurs when attempting to connect to Portal for ArcGIS using the domain name server (DNS) alias and the portal is authenticating through a web-tier authentication (IWA or SAML).

Solution or Workaround

To solve this issue, use the fully qualified domain name (FQDN) to connect to the portal.

gis = GIS("https://<machine.domain.com>:7443/arcgis", "username", "password", verify_cert = False)

Note:
For portals authenticating through web-tier authentication, using the FQDN with port 7443 is the only workaround for this issue, and users are unable to use DNS within the script.