Consume External API in D365FO using .Net library

 using System;

using System.Collections.Generic;

using System.Linq;

using System.Net;

using System.Net.Http;

using System.Net.Http.Headers;

using System.Text;

using System.Threading.Tasks;

using Newtonsoft.Json;

namespace SAN_NotificationsLibrary

{

    public class SAN_NotificationService

    {

        public void ProcessNotification(string userName, string password, string url, string clientId, string clientSecretKey, string customerId, string subject, int days, string body)

        {

            string tokenPath = "/identity/connect/token";

            var uri = new Uri(url); 

            var accessToken = GetAccessToken($"{uri.Scheme}:

            var client = new HttpClient();

            client.BaseAddress = new Uri($"{uri.Scheme}:

            var request = new HttpRequestMessage(HttpMethod.Post, uri.AbsolutePath);

            client.DefaultRequestHeaders.Add("Authorization", "Bearer " + accessToken);

            var data = new

            {

                subject = subject,

                body = body,

                customerNumber = customerId,

                duration = days

            };

            request.Content = new StringContent(JsonConvert.SerializeObject(data), Encoding.UTF8, "application/json");

            var response = client.SendAsync(request).Result;

           

        }

        private string GetAccessToken(string baseUrl, string tokenPath, string clientId, string clientSecret, string userName, string password)

        {

            var client = new HttpClient();

            client.BaseAddress = new Uri(baseUrl);

            var request = new HttpRequestMessage(HttpMethod.Post, tokenPath);

            var byteArray = new UTF8Encoding().GetBytes($"{clientId}:{clientSecret}");

            client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", Convert.ToBase64String(byteArray));

            var postData = new List<KeyValuePair<string, string>>();

            postData.Add(new KeyValuePair<string, string>("grant_type", "password"));

            postData.Add(new KeyValuePair<string, string>("username", userName));

            postData.Add(new KeyValuePair<string, string>("password", password));

            request.Content = new FormUrlEncodedContent(postData);

            var response = client.SendAsync(request).Result;

            var t = response.Content.ReadAsStringAsync().Result;

            var token = JsonConvert.DeserializeObject<Token>(t);

            return token?.AccessToken;

        }

        internal class Token

        {

            [JsonProperty("access_token")]

            public string AccessToken { get; set; }

            [JsonProperty("token_type")]

            public string TokenType { get; set; }

            [JsonProperty("expires_in")]

            public int ExpiresIn { get; set; }

            [JsonProperty("refresh_token")]

            public string RefreshToken { get; set; }

        }

    }

}