Add isSSN API route and function

This one we have to be careful with, because we don't want to encourage sending payloads of sensitive info.

We aren't storing anything in persistence (or at least yet) and we want to make sure the data is not exposed.

Maybe for this one we should consult best practices for security.

Maybe encrypt the payload with the SSN (or require it to come encrypted), decrypt, validate, encrypt, and return a true/false?