AuthConfig.cs

using System;
using System.IO;
using System.Globalization;
using Microsoft.Extensions.Configuration;

namespace CommandAPIClient
{
  public class AuthConfig
  {
    public string Instance {get; set;} = "https://login.microsoftonline.com/{0}";
    public string TenantId {get; set;}
    public string ClientId {get; set;}
    public string Authority
    {
      get
      {
        return String.Format(CultureInfo.InvariantCulture, Instance, TenantId);
      }
    }
    public string ClientSecret {get; set;}
    public string BaseAddress {get; set;}
    public string ResourceID {get; set;}

    public static AuthConfig ReadFromJsonFile(string path)
    {
      IConfiguration Configuration;

      var builder = new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile(path);

      Configuration = builder.Build();

      return Configuration.Get<AuthConfig>();
    }
  }
}