# Integrate the APIs
source: https://developer.mastercard.com/mastercard-checkout-solutions/tutorial/integrate_apis_scof/step2/index.md

## Step 2: Integrate the APIs {#step-2-integrate-the-apis}

* To get started with the API integration, you can generate an API client using an [OpenAPI Generator](https://openapi-generator.tech/), which provides generators and library templates for supporting multiple languages and frameworks.

* To help you sign requests and perform payload encryption/decryption, Mastercard provides [client authentication libraries](https://github.com/Mastercard?q=oauth1-signer) and [encryption libraries](https://github.com/Mastercard?&q=client-encryption).

* Follow the steps in [Generating and Configuring a Mastercard API Client](https://developer.mastercard.com/platform/documentation/security-and-authentication/generating-and-configuring-a-mastercard-api-client/) tutorial to enable authentication and perform encryption/decryption.

* Mastercard supports two protocols for authenticating client applications to integrate with Mastercard APIs. Learn more on /documentation/api-basics/ page.

Note: **In case of OAuth Authentication:**   

* Site identifier `X-Src-Cx-Flow-Id` is added as a part of all inbound API response headers for resolving site affinity issues on subsequent calls.
* When making back-to-back API calls, the client must include the `x-Src-Cx-Flow-Id` of the initial API response in the header of the subsequent API request. This ensures that the consecutive API calls will be sent to the same Mastercard server that returned the initial response.   

**In case of Mutual TLS (MTLS) Authentication:**   

* The `X-Src-Response-Host` containing a site-specific URL is initially sent from Mastercard in response to the client.
* Use this same URL instead of the standard services.mastercard.com domain to ensure that the subsequent calls are directed to the same server that returned the initial response.
* MTLS is an alternate authentication mechanism, available on request. Work with your [Mastercard representative](https://developer.mastercard.com/mastercard-checkout-solutions/documentation/support/index.md#get-help) for details.