Unable to sign in to the Portaladmin API after upgrading to Portal for ArcGIS 10.5.1

Error Message

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.

Cause

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:

Error:   
"Invalid Token"
or
"You are not authorized to access this resource"

Additionally, the Portal logs display messages similar to:

Error:
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

If possible, before upgrading to Portal for ArcGIS 10.5.1, add the forward proxy JavaScript Object Notation (JSON) "nonProxyHosts" parameter to the Portal for ArcGIS system properties.

1. Sign in to the Portaladmin API using an administrator account.
   • Example: https://portal.domain.com:7443/arcgis/portaladmin
2. Select System > Properties > Update (https://portal.domain.com:7443/arcgis/portaladmin/system/properties/update).
3. Add "nonProxyHosts":"portal.domain.com" to the forward proxy settings (replace portal.domain.com with the Fully Qualified Domain Name (FQDN) of the machine Portal for ArcGIS is installed on. 
   • Example: 

"httpProxyHost":"forwardproxy.domain.com","httpsProxyHost":"forwardproxy.domain.com","httpProxyPort":80,"httpsProxyPort":443","nonProxyHosts":"portal.domain.com"

• This is further explained in the Web Help documentation, Using a forward proxy server with Portal for ArcGIS.

4. Select Update Properties to save the changes.
5. Sign out of Portal for ArcGIS. The application restarts.
6. Once Portal for ArcGIS has finished restarting, sign back in to Portaladmin to verify the settings were saved.
7. Create a backup using the ArcGIS Enterprise backup utility.
8. Once the backup is complete, upgrade to Portal for ArcGIS 10.5.1.

• Contact Esri Technical Support to receive assistance with reverting Portal for ArcGIS back to the previous version, or
• Modify the catalina.properties and portal-config.properties pages, as follows:

1. Stop the Portal for ArcGIS Windows Service in the Services console (services.msc):
   • From the Run dialog, type services.msc, and press Enter.
2. Create a backup copy of the catalina.properties file, for example:
   <C:\Program Files\ArcGIS\Portal\framework\runtime\tomcat\conf\catalina.properties>
3. Using a text editor, open the catalina.properties file.
4. Comment out the following entries:
   • http.proxyHost =
   • https.proxyHost =
   • http.proxyPort =
   • https.proxyPort =
   • nonProxyHosts =
5. Save the catalina.properties file
6. Create a backup copy of the portal-config.properties file, for example:
   <C:\Program Files\ArcGIS\Portal\framework\etc\portal-config.properties>
7. Using a text editor open the portal-config.properties file.
8. Comment out the following entries:
   • http.proxyHost =
   • https.proxyHost =
   • http.proxyPort =
   • https.proxyPort =
   • nonProxyHosts =
9. Save the portal-config.properties file.
10. Start the Portal for ArcGIS Windows services in the Services console (services.msc).
11. Sign into the Portal for ArcGIS Portaladmin API (https://portal.domain.com:7443/arcgis/portaladmin)
12. Select System > Properties > Update.
13. Add "nonProxyHosts":"portal.domain.com". Replace portal.domain.com with the hostname that Portal for ArcGIS is installed on. For example:

• "httpProxyHost":"forwardproxy.domain.com","httpsProxyHost":"forwardproxy.domain.com","httpProxyPort":80,"httpsProxyPort":443","nonProxyHosts":"portal.domain.com"

14. Select Update Properties.
15. Create a backup using the ArcGIS Enterprise backup utility.