For more information about Basic Auth, please read the IETF.org article about authentication .
Using Basic Authentication is the simplest way to implement the authentication process for your application. Simply provide a username and password string with base64 encoding in the Authentication Header and call the APIs' endpoints on the same request. You can also use your consumer key and secret with base64 encoding. The Checkout API uses HTTP Basic Authentication over an SSL layer for security protection.
Example Request Header for Basic:
POST https://api.mxmerchant.com/checkout/v3/payment?echo=true HTTP/1.1 Authorization: Basic dWF0cG9zdG1hbjpUZW1wMTU1MTU1MTU1== Content-Type:application/json; charset=utf-8