To me you have two problems here not just one. SharePoint SSS (Secure Store Service) is an SSO (Single Sign on) database. Are you asking for a database to store ID's which can be retrieved from an Application ID or are you trying to secure SSS
numbers? Their are many different SSO's out there. If you want more on single sign on.
Look here for more on single sign on (Not SharePoint.)
https://msdn.microsoft.com/en-us/library/aa745042(v=bts.10).aspx
Microsoft's Enterprise single sign-on.
https://msdn.microsoft.com/en-us/library/gg167084.aspx
If you are looking simply to store you SSS ID's then I would just create a sql database and limit the permissions to who can use it.
Good luck,
Gary