AuthenticationConfig.cs

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

namespace MyAadFunction
{
    public class Config
    {
        /// <summary>
        /// instance of Azure AD, for example public Azure or a Sovereign cloud (Azure China, Germany, US government, etc ...)
        /// </summary>
        public string Instance { get; set; } = "https://login.microsoftonline.com/{0}";

        /// <summary>
        /// Graph API endpoint, could be public Azure (default) or a Sovereign cloud (US government, etc ...)
        /// </summary>
        public string ApiUrl { get; set; } = "https://graph.microsoft.com/";

        /// <summary>
        /// Reads the configuration from a json file
        /// </summary>
        /// <param name="path">Path to the configuration json file</param>
        /// <returns>AuthenticationConfig read from the json file</returns>
        public static Config ReadFromJsonFile(string path)
        {
            IConfigurationRoot Configuration;

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

            Configuration = builder.Build();
            return Configuration.Get<Config>();
        }
    }
}