# Reference Application
source: https://developer.mastercard.com/cross-border-services/documentation/ref-app/index.md

You may connect to the Mastercard Cross-Border Services APIs either using a **REST client**.
Below tutorials illustrates the available options to connect to the Cross-Border Service APIs in the Sandbox environment with OAuth1.0A and OAuth2.0:

| Authentication Mechanism |      Option       |            APIs             |                                                                                          Tutorials                                                                                           |
|--------------------------|-------------------|-----------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| OAuth1.0A                | using REST client | All APIs                    | [Reference Application Tutorial using OAuth1.0A](https://developer.mastercard.com/cross-border-services/documentation/ref-app/reference-app-tutorial/index.md)                               |
| OAuth2.0                 | using REST client | All APIs except Balance API | [Reference Tutorial for Request Token based OAuth2.0](https://developer.mastercard.com/cross-border-services/documentation/ref-app/oauth2-reference-app-tutorial-request-token/index.md)     |
| OAuth2.0                 | using REST client | Balance API                 | [Reference Tutorial for Authorization Code based OAuth2.0](https://developer.mastercard.com/cross-border-services/documentation/ref-app/oauth2-reference-app-tutorial-access-token/index.md) |

Alert: If you are a Customer contracted with MTS EU or MTS UK, you must connect using [OAuth2.0 Authorization Code flow](https://developer.mastercard.com/cross-border-services/documentation/oauth2-access-token-based-authentication-details/index.md) for Balance API and [OAuth2.0 Request Token based flow](https://developer.mastercard.com/cross-border-services/documentation/oauth2-request-token-based-authentication-details/index.md) for all APIs (except Balance API) as the authentication mechanism to ensure compliance with the relevant jurisdiction based Regulatory Technical Standards (either EU or UK) derived from the Revised Payment Services Directive (PSD2).  

You may look at [Getting Started with APIs using OAuth2.0](https://developer.mastercard.com/cross-border-services/documentation/api-basics/getting-started-oauth2/index.md) for step by step instructions on how to setup with OAuth2.0.

These tutorials show how you could use the Cross-Border Service APIs, but they do not prescribe the design and interactions of your funds transfer solution; those aspects are for you to define.