How to get refreshed token when connecting with PowerBI Desktop to REST API Power BI

Hi, 

I need your help to find the exact syntax in order to get a refreshed token to connect to the Power BI Rest API with Power BI desktop.

I can get a temporary token using the try function with this link : https://learn.microsoft.com/en-us/rest/api/power-bi/reports/get-reports-in-group

But I need to dynamically refresh the token in order use the API with a valid token at each refresh.

I tried the code below but it doesn't work (changing the ***** and common with the tenant ID) :

the code : 

() =>
let
body = "grant_type=Password&resource=https://analysis.windows.net/powerbi/api&client_id=****&username=***.onmicrosoft.com&password=*****",
Data=Json.Document(Web.Contents("https://login.microsoftonline.com/common/oauth2/token/", [Headers=[#"Content-Type"="application/x-www-form-urlencoded"], Content=Text.ToBinary(body)])),
access_token = Data[access_token]
in
access_token

many thanks for those who can help me.

Regards, 

GJA