The Payment Provider Gateway documentation uses the Magento 2.3.x version of the Braintree module as a reference application. The Braintree module was removed in Magento 2.4.0. The concepts described in this guide are still applicable to Magento 2.4.0, but the code samples are not supported.
This is a beta release of documentation for Magento 2.4, published for previewing soon-to-be-released functionality. Content in this version is subject to change. Links to the v2.4 code base may not properly resolve until the code is officially released.

Request Builder

Request Builder is a component of the Magento payment gateway responsible for building a request from several parts. It allows implementing complex, yet atomic and testable, building strategies. Each builder can have simple logic or contain builder composites.

Basic interface

The basic interface for a request builder is \Magento\Payment\Gateway\Request\BuilderInterface.

Builder composite

\Magento\Payment\Gateway\Request\BuilderComposite is a container for a list of \Magento\Payment\Gateway\Request\BuilderInterface implementations. It gets a list of classes, or types, or virtual type names, and performs a lazy instantiation on an actual BuilderComposite::build([]) call. So that you can have as many objects, as required, but only those, which are needed for a request are instantiated.

BuilderComposite implements the composite design pattern.

The concatenation strategy is defined in the BuilderComposite::merge() method. So if you need to alter the strategy, you need to add your custom implementation of BuilderComposite.

Adding a builder composite

Builder composites are added using dependency injection in di.xml. A builder composite might comprise simple builders as well as other builder composites.

Example of adding composite builders for the Braintree payment provider (app/code/Magento/Braintree/etc/di.xml):

<!--  is a builder composite comprising a number of builders -->
<virtualType name="BraintreeAuthorizeRequest" type="Magento\Payment\Gateway\Request\BuilderComposite">
        <argument name="builders" xsi:type="array">
            <item name="customer" xsi:type="string">Magento\Braintree\Gateway\Request\CustomerDataBuilder</item>
            <item name="payment" xsi:type="string">Magento\Braintree\Gateway\Request\PaymentDataBuilder</item>
            <item name="channel" xsi:type="string">Magento\Braintree\Gateway\Request\ChannelDataBuilder</item>
            <item name="address" xsi:type="string">Magento\Braintree\Gateway\Request\AddressDataBuilder</item>
            <item name="vault" xsi:type="string">Magento\Braintree\Gateway\Request\VaultDataBuilder</item>
            <item name="3dsecure" xsi:type="string">Magento\Braintree\Gateway\Request\ThreeDSecureDataBuilder</item>
            <item name="device_data" xsi:type="string">Magento\Braintree\Gateway\Request\KountPaymentDataBuilder</item>
            <item name="dynamic_descriptor" xsi:type="string">Magento\Braintree\Gateway\Request\DescriptorDataBuilder</item>
            <item name="store" xsi:type="string">Magento\Braintree\Gateway\Request\StoreConfigBuilder</item>
            <item name="merchant_account" xsi:type="string">Magento\Braintree\Gateway\Request\MerchantAccountDataBuilder</item>
<!-- The same BraintreeAuthorizeRequest builder composite is a part of the BraintreeSaleRequest builder composite -->
<virtualType name="BraintreeSaleRequest" type="Magento\Payment\Gateway\Request\BuilderComposite">
        <argument name="builders" xsi:type="array">
            <item name="authorize" xsi:type="string">BraintreeAuthorizeRequest</item>
            <item name="settlement" xsi:type="string">Magento\Braintree\Gateway\Request\SettlementDataBuilder</item>