Looking for the most elegant way to both serve my ads to a client's site, and then verify their identity when they use my service.
1. Serve ad via javascript to client site (www.client.com) , and serve a uid inside a form, and a form itself:
AD HERE
<form action="www.client.com/theyWriteThis">
<input type='hidden' name='uid' value="1234">
<input type='text' name="something">
<input type='submit'>
</form>
2. Client will get the UID, then send another userId back to me. The combination of UID and userid will prove their identity to me.