How to create a sss or ssn validator

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PHP

hello guys im trying to create a validation form that will check or validate if the user that registered is an OFW or not... and im thinking to ask for their SSS or SSN number but im not sure how to validate if this number is valid or not? Do php have a third party application that can be integrated on my site to make this work? like for this site http://www.ssnvalidator.com/[^]
it seems to be working like i want it... but do you have any ideas on how to use this third party and retrieved the information or confirmation that says the number they inputted is valid