Customer and Payment API Extensions
You can now extend the behavior of the Payment API and the Customer API with your business logic with the help of API Extensions. An API Extension gets called after the processing of a create or update request of an API call but before the result is persisted. The API Extension can validate the object or apply additional updates to it. It can, for example, validate that a payment in the given configuration can be processed, or trigger actions with the Payment Service Provider (PSP). Or it can validate that a customer's account details don't look fraudulent, or set a customer group based on the email address.
To get started with API Extensions, you can read the tutorial.