It would be great to obtain a valid SSL certificate directly from FileMaker Inc.
I don't care if I have to pay for it but I'd be sure that it's valid, it's trustable and it should be super easy to setup, request and install. For example:
1.- Click on request SSL certificate.
2.- Choose between the different options (wildcard, single domain, etc.).
3.- Input your information.
4.- Choose your payment method.
5.- Generate and install.
FileMaker Server should generate the certificate, automatically install it and give you a download link, just in case.
It would be perfect if that's for free, but we all know there's no free lunch, so I'd be more than happy if the process would be automatic, simple and directly with FMI.