問題

Dataverse APIを呼び出す時、アクセストークンの取得は必要があります。
MS認証を実装したら、いつもAADSTS50076エラーを返してきます。
エラーを確認すると、二重認証でアクセストークンが取得できませんっていうことです。
AADSTS50076: Due to a configuration change made by your administrator, or because you moved to a new location, you must use multi-factor authentication to access '00000001-0000-0000-c000-000000000000'.

解決方法

あるアカウントの二重認証を外して、かつ、管理者権限を付与する。そのアカウントでアクセストークンを取得します。

サンプルコード

※XXXXXXXは自分の情報を入れてください

using Microsoft.IdentityModel.Clients.ActiveDirectory;
using System.Net.Http.Headers;
using System.Net.Http;
using System;
using static System.Console;

namespace ConsoleApp2
{
     class testClass
    {

        /// <summary>
        /// Holds the Authentication context based on the Authentication URL
        /// </summary>
        static AuthenticationContext authContext;

        /// <summary>
        /// Holds the actual authentication token once after successful authentication
        /// </summary>
        static AuthenticationResult authToken;

        static string apiUrl = "https://XXXXX.api.crm.dynamics.com/api/data/v9.2";

        /// <summary>
        /// Client ID or Application ID of the App registration in Azure
        /// </summary>
        static string clientId = "XXXXXXXXXXX";

        /// <summary>
        /// The Redirect URL which we defined during the App Registration
        /// </summary>
        static string redirectUrl = "http://localhost/";

        static string userId = "XXXX@XXXX.onmicrosoft.com";

        static string password = "XXXXXXXX";

         public static async void GetToken()
        {
            AuthenticationParameters ap = AuthenticationParameters.CreateFromResourceUrlAsync(new Uri(apiUrl)).Result;
            string resourceUrl = ap.Resource;
            string authorityUrl = ap.Authority;
            authContext = new AuthenticationContext(authorityUrl, false);
            UserCredential credentials =
            new UserPasswordCredential(userId, password);
            //Genertae the AuthToken by using Credentials object.
            authToken = await authContext.AcquireTokenAsync
            (resourceUrl, clientId, credentials);
            WriteLine("Got the authentication token, Getting data from Webapi !!");
            GetData(authToken.AccessToken);
        }

        public static async void GetData(string token)
        {
            using (HttpClient httpClient = new HttpClient())
            {
                httpClient.Timeout = new TimeSpan(0, 2, 0);  // 2 minutes time out period.
                                                             // Pass the Bearer token as part of request headers.
                httpClient.DefaultRequestHeaders.Authorization =
                new AuthenticationHeaderValue("Bearer", token);
                var data = await httpClient.GetAsync("https://XXXXXXX.api.crm.dynamics.com/api/data/v9.2/accounts?$select=name");
                if (data.StatusCode == System.Net.HttpStatusCode.OK)
                {
                    WriteLine(await data.Content.ReadAsStringAsync());
  
                    JObject body = JObject.Parse(
                    data.Content.ReadAsStringAsync().Result);
  
                    Console.WriteLine(body);
                }
                else
                {
                    WriteLine($"Some thing went wrong with the data retrieval. Error code : {data.StatusCode} ");
                }
                ReadLine();
            }
        }

    }

}

ソース実行結果

注意点

取得結果が空の場合は、アカウントを管理者権限が付与されていない可能性があります。