This is a sample Controller for obtaining a token for Immersive Reader Cognitive Service

Immersive Reader (Cognitive Service) Controller

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using ImmersiveReaderDemo.Models;
using Microsoft.IdentityModel.Clients.ActiveDirectory;

namespace ImmersiveReaderDemo.Controllers
{
    public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;
        private readonly string TenantId;     // Azure subscription TenantId
        private readonly string ClientId;     // Azure AD ApplicationId
        private readonly string ClientSecret; // Azure AD Application Service Principal Client Secret
        private readonly string Subdomain;    // Immersive Reader resource subdomain (resource 'Name' if the resource was created in the Azure portal, or 'CustomSubDomain' option if the resource was created with Azure CLI Powershell. Check the Azure portal for the subdomain on the Endpoint in the resource Overview page, for example, 'https://[SUBDOMAIN].cognitiveservices.azure.com/')

        public HomeController(ILogger<HomeController> logger, Microsoft.Extensions.Configuration.IConfiguration configuration)
        {
            _logger = logger;
            TenantId = configuration["TenantId"];
            ClientId = configuration["ClientId"];
            ClientSecret = configuration["ClientSecret"];
            Subdomain = configuration["Subdomain"];
        }

        public IActionResult Index()
        {
            return View();
        }

        [ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
        public IActionResult Error()
        {
            return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
        }

        [Route("subdomain")]
        public string GetSubdomain()
        {
            return Subdomain;
        }

        [Route("token")]
        public async Task<string> GetToken()
        {
            return await GetTokenAsync();
        }

        /// <summary>
        /// Get an Azure AD authentication token
        /// </summary>
        private async Task<string> GetTokenAsync()
        {
            string authority = $"https://login.windows.net/{TenantId}";
            const string resource = "https://cognitiveservices.azure.com/";

            AuthenticationContext authContext = new AuthenticationContext(authority);
            ClientCredential clientCredential = new ClientCredential(ClientId, ClientSecret);

            AuthenticationResult authResult = await authContext.AcquireTokenAsync(resource, clientCredential);

            return authResult.AccessToken;
        }
    }
}