Adding custom vars to email templates? User email confirmation FRONTEND_URL use case

I was checking the code and it seems that the isValidTemplate function only accepts these values:

const authorizedKeys = [
‘URL’,
‘ADMIN_URL’,
‘SERVER_URL’,
‘CODE’,
‘USER’,
‘USER.email’,
‘USER.username’,
‘TOKEN’,
];

I’m guessing it is for security reasons, for now I will hard code my values inside the mails, although I think it is not ideal.