Returns the tenant id and api code from a user slug.
Shortcut call: credentials https://api.artlookonline.com/credentials/pablo-picasso
https://api.artlookonline.com/credentials/pablo-picasso
(array of tenant_id and api_code) EG: {"tenant_id":154,"api_code":"ILZDaB!"}
{"tenant_id":154,"api_code":"ILZDaB!"}