Responsive web payment

This scenario is the most common integration for webshops that don't need any extra steps in the payment process.

The payment process

1. In this scenario the payment starts with the preparation of the payment. This means that the webshop creates a JSON representation of the payment data. This data contains all the necessary information about the items to be purchased, the customer and the desired payment scenario. This JSON should be sent as the body of a POST request to the /v2/Payment/Start API endpoint. After the system recives the data it will be validated. If all the properties are correct a payment will be prepared in the database and a HTTP response is returned to the webshop.
2. The response should be processed by the webshop system and the Id of the payment (PaymentId) should be extracted from the response. This Id should be stored in the webshop database with the initial information about the payment. This is necessary because every following request is based on this Id.
3. The next step is to redirect the customer to the Barion website to a specific URL with the PaymentId as a query parameter.
4. After the customer paid the requested amount and the payment is completed a server to server request is initiated by Barion towards the webshop. This is called the callback mechanism.
5. At this point the customer is advised on the screen to return to the webshop to complete the process. If the customer clicks through the customer is redirected back to the webshop.
6. At any point of the process the webshop can request information about the payment through the v2/Payment/GetPaymentState API endpoint.

Preparing the payment

Assembling the POST request

TODO

Processing the response

TODO

Redirecting the customer

TODO

Processing the callback

TODO

Requesting information about the payment

TODO

Processing the returning customer

TODO