As mentioned in the Product Roadmap for 2017...
Purchase SSL certificates from the FileMaker Store and automatically install them on FileMaker Server.
Please, please, please add this feature (while not charging an arm and a leg for it)!
This would save so much time and trouble that it would be worth a reasonable premium over existing SSL certs. I imagine the hours saved in support calls by FileMaker would probably pay for the development costs.
Everyone's life would be easier.