Error: Unable to sign in to the Portaladmin API after upgrading to Portal for ArcGIS 10.5.1
If Portal for ArcGIS is upgraded to version 10.5.1 while the previously installed version has a forward proxy server configured, the user can sign in to the Portal for ArcGIS home application and Sharing API, but not the Portaladmin API.
The Portaladmin API is unable to authenticate through the specified forward proxy server. When attempting to sign in, one of the following errors occurs in the web browser:
"You are not authorized to access this resource"
Additionally, the Portal logs display messages similar to:
Failed to generate a token for user 'portaladmin'. java.lang.Exception: Server returned HTTP status code 404. Requested URL: https://portaladmin.domain.com:7443/arcgis/sharing/generateToken
Solution or Workaround
Sign in to the Portaladmin API using an administrator account.