msal.cs

// See https://aka.ms/new-console-template for more information
using Microsoft.Identity.Client;

var app = ConfidentialClientApplicationBuilder
    .Create("a43255e1-24df-4b22-94e9-4e583e6301c3")
    .WithClientSecret("RKP8Q~LKTGJKwzsItxnpIfIVG2XMAyPG1IhvIcpk")
    .WithAuthority(new Uri("https://login.microsoftonline.com/81699cc3-1e16-40c8-afb9-5b4e2aac2dca"))
    .Build();

var token = await app.AcquireTokenForClient(new[]
{
    //"api://428397d6-f39f-414e-ae5b-6b352e086aba/.default"
    //"https://graph.microsoft.com/.default"
    //"api://7589631c-d6ec-4674-889d-3ac60d7592ab/.default"
    //"api://backend-application2/.default"
    "api://8c09a569-597a-49c4-beb7-54077f767b43/.default"
}).ExecuteAsync();

Console.WriteLine(token.AccessToken);