Android certificate install:
1. Download the file Fortinet_CA_SSL.cer and, when it completes, open to install.
2. A "Name the certificate" box will open. I suggest "STMA" for the name. set credential use to VPN and apps. Click OK.
3. Since this is a private root CA, Android will warn you with a notification that the "Network may be monitored." This is true only of the STMA network, not other networks you connect to. the warning can be safely swiped away, but it may pop up again from time to time.
If you are unable to download from this site (the chrome browser on some android devices blocks the download). You can get the Cert through drive with this link: Drive: Fortinet_CA_SSL.cer.