The server you are trying to connect cannot be verified

Error Message

Attempting to log in to an ArcGIS Enterprise portal using Collector for ArcGIS (Android) version 17.0.4 and above, or attempting to access the Portal for ArcGIS home page using an Android device, returns the following error message:

Error:   
The server you are trying to connect cannot be verified.

Cause

An Android device does not have the capability to bypass certificate authentication like a computer. By default, only certain certificate authority (CA) certificates that are pre-installed in Android operating systems meet Android security requirements. Therefore, the CA certificates used by Portal for ArcGIS must be installed manually in the Android device.

To check if the CA certificates used by Portal for ArcGIS are trusted on an Android device, refer to the Work with CA certificates (trusted credentials) section in Google Support: Add & remove certificates.

Solution or Workaround

To establish trust between Collector for ArcGIS (Android) and Portal for ArcGIS, the CA certificates used by Portal for ArcGIS and the web server certificate must be installed in the Android device manually. To do so, follow the steps described below:

1. Export the root certificate and all the intermediate certificates (CA certificates) from Portal for ArcGIS on the desktop. For steps to do so, refer to How To: Export Certificates from ArcGIS Server and Portal for ArcGIS.

Note:
Ensure the root certificate, and all the intermediate certificates are saved as files with .cer extension.

2. Export the certificate from the web server hosting portal's ArcGIS Web Adaptor on the desktop. For example, for IIS Web Server, refer to Microsoft Web Help: Export the Private Key Portion of a Server Authentication Certificate.

Note:
Ensure this certificate is saved as a file with .pfx extension.

3. Manually install all the exported certificates on the Android device. To manually import certificates on an Android device, refer to the following document, Google Support: Add & remove certificates.