ProtectedApiCallHelper.cs

// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License.

using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System;
using System.Linq;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;

namespace MyAadFunction
{
    /// <summary>
    /// Helper class to call a protected API and process its result
    /// </summary>
    public class ProtectedApiCallHelper
    {
        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="httpClient">HttpClient used to call the protected API</param>
        public ProtectedApiCallHelper(HttpClient httpClient)
        {
            HttpClient = httpClient;
        }

        protected HttpClient HttpClient { get; private set; }


        /// <summary>
        /// Calls the protected web API and processes the result
        /// </summary>
        /// <param name="webApiUrl">URL of the web API to call (supposed to return Json)</param>
        /// <param name="accessToken">Access token used as a bearer security token to call the web API</param>
        /// <param name="processResult">Callback used to process the result of the call to the web API</param>
        public async Task<JObject> CallWebApiAndProcessResultASync(string webApiUrl, string accessToken)
        {
            if (!string.IsNullOrEmpty(accessToken))
            {
                var defaultRequestHeaders = HttpClient.DefaultRequestHeaders;
                if (defaultRequestHeaders.Accept == null || !defaultRequestHeaders.Accept.Any(m => m.MediaType == "application/json"))
                {
                    HttpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                }
                defaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);

                HttpResponseMessage response = await HttpClient.GetAsync(webApiUrl);
                if (response.IsSuccessStatusCode)
                {
                    string json = await response.Content.ReadAsStringAsync();
                    JObject result = JsonConvert.DeserializeObject(json) as JObject;
                    return result;
                }
                else
                {
                    string content = await response.Content.ReadAsStringAsync();

                    // Note that if you got reponse.Code == 403 and reponse.content.code == "Authorization_RequestDenied"
                    // this is because the tenant admin as not granted consent for the application to call the Web API
                    throw new Exception($"Failed to call the web API: {response.StatusCode}\nContent: {content}");
                }
            }

            return null;
        }
    }
}