Adding a trusted certificate for FortiSSLVPN in NetworkManager

I needed to connect to a Fortinet SSLVPN, but the certificate on it had expired. While the official Mac client prompts and lets you connect anyways, Linux with NetworkManager (and the FortiSSLVPN plugin) would refuse without providing any messages. Unfortunately, I couldn’t ask the administrator to renew the certificate. What you can do is add the certificate as a trusted certificate for that VPN. Unfortunately, the interface to do this is unclear, so I’ll try to explain it here.

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