Call remote API from Azure Function with Managed Identity

function.cs

using System;
using System.IO;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;
using Azure.Identity;
using Microsoft.Azure.Services.AppAuthentication;
using System.Net.Http;

namespace lighthousefunc
{
    public static class HttpTrigger
    {
        [FunctionName("HttpTrigger")]
        public static async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
            ILogger log)
        {
            log.LogInformation("C# HTTP trigger function processed a request.");

            string audience = "https://management.azure.com";
            //var token = new DefaultAzureCredential();
            AzureServiceTokenProvider tokenProvider = new AzureServiceTokenProvider();
            string accessToken = await tokenProvider.GetAccessTokenAsync(audience);
            log.LogInformation($"Successfully acquired access token from Managed Identity: {accessToken.Substring(0,10)}");

            // We have the access token let's call ARM API

            try
            {
                string targetAPI = "https://management.azure.com/subscriptions?api-version=2020-01-01";
                HttpClient c = new HttpClient();
                c.DefaultRequestHeaders.Add("Authorization", $"Bearer {accessToken}");
                string response = await c.GetStringAsync(targetAPI);

                return new OkObjectResult(response);
            }
            catch (Exception ex)
            {
                log.LogError($"Error calling remote REST API: {ex.Message}");

                return new BadRequestObjectResult($"Function called the remote REST API but response was not success: {ex.Message}");
            }
    
        }
    }
}