post https://sandbox.array.io/api/user/v2
When one of your customers uses your app to enroll in Array, you must create a User object for that customer by calling the Create a User operation. If the object is successfully created, the operation returns a clientKey token that identifies the new object. You'll use this token when you call most of the other Array operations. For example, when you order a credit report for a customer, you must pass in the customer's clientKey.
It's your responsibility to map the clientKey token to your own representation of the customer, and to store the token securely.