Pull data from API using POST method in Power BI

Hi all, I'm a fresher in Power BI Desktop. my mission is extract data from given credentials include: ClientID, Password and Url. The credentials must be Base64 encoded for use in the POST /oauth2/token request. I have used that credentials in Postman and I got its header such as: Authorization: Basic xxxxxxxxxxxxxxxxxxxxxx. what should i start with all of them to get data from API. Can anyone help me to solve this probleml. thank you so much for any solution and suggestion. Cheer!!!