I'm trying to set up a security certificate for a sql server. According to the documentation, I need to set up the permissions so that the sql server instance can read the private key. I tried setting up the permissions through mmc (see https://stackoverflow.com/questions/36830411/how-can-i-give-sql-server-permission-to-read-my-ssl-key). I right click on the cert, select 'all tasks', select 'manage private keys', and it brings up the users dialog. The problem is, the sql server instance is running as 'NT Service\MSSQLSERVER'. That user doesn't appear in the group or user names section and I can't find it if I try to add it as a new user.
I tried the procedure listed here: How to add NETWORK SERVICE to Users permission group? but I still wasn't able to find that user or group. What am I doing wrong here?