Isolated Azure Function Authentication via Code

Yes, you can make use of Azure.Identity in Azure Functions Isolated Trigger like below:-

I am using Azure.Identity from Azure Isolated Function to get the List of Resource group from my Function Trigger using Client Credentials flow:-

Function1.cs:-

using System.Net;
using Microsoft.Azure.Functions.Worker;
using Microsoft.Extensions.Logging;
using System.Threading.Tasks;
using Azure.Core;
using Azure.Identity;
using System.Net.Http;
using Microsoft.Azure.Functions.Worker.Http;
using Newtonsoft.Json;

namespace FunctionApp1
{
    public class Function1
    {
        private readonly ILogger<Function1> _logger;
        private readonly IHttpClientFactory _httpClientFactory;

        public Function1(ILogger<Function1> logger, IHttpClientFactory httpClientFactory)
        {
            _logger = logger;
            _httpClientFactory = httpClientFactory;
        }

        [Function("Function1")]
        public async Task<HttpResponseData> RunAsync(
            [HttpTrigger(AuthorizationLevel.Function, "get", "post")] HttpRequestData req,
            FunctionContext executionContext)
        {
            _logger.LogInformation("C# HTTP trigger function processed a request.");

            var token = await GetAccessToken("TENANT-ID", "CLIENT-ID", "CLIENT-SECRET");
            var results = await GetResults(token);

            var response = req.CreateResponse(HttpStatusCode.OK);
            response.Headers.Add("Content-Type", "application/json; charset=utf-8");

            await response.WriteStringAsync(JsonConvert.SerializeObject(results));

            return response;
        }

        private static async Task<string> GetAccessToken(string tenantId, string clientId, string clientKey)
        {
            var credentials = new ClientSecretCredential(tenantId, clientId, clientKey);
            var result = await credentials.GetTokenAsync(new TokenRequestContext(new[] { "https://management.azure.com/.default" }), default);
            return result.Token;
        }

        private async Task<string> GetResults(string token)
        {
            var httpClient = _httpClientFactory.CreateClient();
            httpClient.BaseAddress = new Uri("https://management.azure.com/");

            string subscriptionId = "0151c365-f598-44d6-b4fd-e2b6e97cb2a7";
            string apiVersion = "2021-04-01";

            string URI = $"subscriptions/{subscriptionId}/resourcegroups?api-version={apiVersion}";

            httpClient.DefaultRequestHeaders.Remove("Authorization");
            httpClient.DefaultRequestHeaders.Add("Authorization", "Bearer " + token);

            var response = await httpClient.GetAsync(URI);

            if (response.IsSuccessStatusCode)
            {
                var content = await response.Content.ReadAsStringAsync();
                return content;
            }
            else
            {
                // Handle the error response here
                return "Error: " + response.StatusCode.ToString();
            }
        }
    }
}

Program.cs:-

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

var host = new HostBuilder()
    .ConfigureFunctionsWebApplication()
    .ConfigureServices(services =>
    {
        services.AddApplicationInsightsTelemetryWorkerService();
        services.AddHttpClient(); // Adding IHttpClientFactory
    })
    .Build();

host.Run();

Output:-

Browser:-

Reference:- azure - Call Microsoft Graph API with Function App that is linked to a Static Web App - Stack Overflow