Add endpoint for getting id token for payer

modules/ppcp-api-client/services.php

@@ -9,6 +9,7 @@ declare(strict_types=1);
 
 namespace WooCommerce\PayPalCommerce\ApiClient;
 
+use WooCommerce\PayPalCommerce\ApiClient\Authentication\UserIdToken;
 use WooCommerce\PayPalCommerce\ApiClient\Helper\FailureRegistry;
 use WooCommerce\PayPalCommerce\Common\Pattern\SingletonDecorator;
 use WooCommerce\PayPalCommerce\ApiClient\Endpoint\BillingSubscriptions;
@@ -862,4 +863,11 @@ return array(
 			return new PurchaseUnitSanitizer( $behavior, $line_name );
 		}
 	),
+	'api.user-id-token'                         => static function( ContainerInterface $container ): UserIdToken {
+		return new UserIdToken(
+			$container->get( 'api.host' ),
+			$container->get( 'api.bearer' ),
+			$container->get( 'woocommerce.logger.woocommerce' )
+		);
+	},
 );

modules/ppcp-api-client/src/Authentication/UserIdToken.php

@@ -0,0 +1,92 @@
+<?php
+/**
+ * Generates user ID token for payer.
+ *
+ * @package WooCommerce\PayPalCommerce\ApiClient\Authentication
+ */
+
+namespace WooCommerce\PayPalCommerce\ApiClient\Authentication;
+
+use Psr\Log\LoggerInterface;
+use WooCommerce\PayPalCommerce\ApiClient\Endpoint\RequestTrait;
+use WooCommerce\PayPalCommerce\ApiClient\Exception\PayPalApiException;
+use WooCommerce\PayPalCommerce\ApiClient\Exception\RuntimeException;
+use WP_Error;
+
+/**
+ * Class UserIdToken
+ */
+class UserIdToken {
+
+	use RequestTrait;
+
+	/**
+	 * The host.
+	 *
+	 * @var string
+	 */
+	private $host;
+
+	/**
+	 * The bearer.
+	 *
+	 * @var Bearer
+	 */
+	private $bearer;
+
+	/**
+	 * The logger.
+	 *
+	 * @var LoggerInterface
+	 */
+	private $logger;
+
+	/**
+	 * UserIdToken constructor.
+	 *
+	 * @param string          $host The host.
+	 * @param Bearer          $bearer The bearer.
+	 * @param LoggerInterface $logger The logger.
+	 */
+	public function __construct(
+		string $host,
+		Bearer $bearer,
+		LoggerInterface $logger
+	) {
+		$this->host   = $host;
+		$this->bearer = $bearer;
+		$this->logger = $logger;
+	}
+
+	/**
+	 * Returns `id_token` which uniquely identifies the payer.
+	 *
+	 * @throws PayPalApiException If the request fails.
+	 * @throws RuntimeException If something unexpected happens.
+	 */
+	public function id_token(): string {
+		$bearer = $this->bearer->bearer();
+		$url    = trailingslashit( $this->host ) . 'v1/oauth2/token?grant_type=client_credentials&response_type=id_token';
+
+		$args = array(
+			'method'  => 'POST',
+			'headers' => array(
+				'Authorization' => 'Bearer ' . $bearer->token(),
+				'Content-Type'  => 'application/x-www-form-urlencoded',
+			),
+		);
+
+		$response = $this->request( $url, $args );
+		if ( $response instanceof WP_Error ) {
+			throw new RuntimeException( $response->get_error_message() );
+		}
+
+		$json        = json_decode( $response['body'] );
+		$status_code = (int) wp_remote_retrieve_response_code( $response );
+		if ( 200 !== $status_code ) {
+			throw new PayPalApiException( $json, $status_code );
+		}
+
+		return $json->id_token;
+	}
+}