How to call a downstream web API from a daemon app

.NET daemon apps can call a web API. .NET daemon apps can also call several preapproved web APIs.

Calling a web API from a daemon application

Here's how to use the token to call an API:

Microsoft.Identity.Web abstracts away the complexity of MSAL.NET. It provides you with higher-level APIs that handle the internals of MSAL.NET for you, such as processing Conditional Access errors, caching.

Here's the Program.cs of the daemon app calling a downstream API:

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Identity.Abstractions;
using Microsoft.Identity.Web;

// In the Program.cs, acquire a token for your downstream API

var tokenAcquirerFactory = TokenAcquirerFactory.GetDefaultInstance();
tokenAcquirerFactory.Services.AddDownstreamApi("MyApi",
    tokenAcquirerFactory.Configuration.GetSection("MyWebApi"));
var sp = tokenAcquirerFactory.Build();

var api = sp.GetRequiredService<IDownstreamApi>();
var result = await api.GetForAppAsync<IEnumerable<TodoItem>>("MyApi");
Console.WriteLine($"result = {result?.Count()}");

Here's the Program.cs of a daemon app that calls Microsoft Graph:

var tokenAcquirerFactory = TokenAcquirerFactory.GetDefaultInstance();
tokenAcquirerFactory.Services.AddMicrosoftGraph();
var serviceProvider = tokenAcquirerFactory.Build();
try
{
    GraphServiceClient graphServiceClient = serviceProvider.GetRequiredService<GraphServiceClient>();
    var users = await graphServiceClient.Users
        .GetAsync(r => r.Options.WithAppOnly());
    Console.WriteLine($"{users.Count} users");
    Console.ReadKey();
}
catch (Exception ex) { Console.WriteLine("We could not retrieve the user's list: " + $"{ex}"); }

Calling several APIs

For daemon apps, the web APIs that you call need to be preapproved. There's no incremental consent with daemon apps. (There's no user interaction.) The tenant admin needs to provide consent in advance for the application and all the API permissions. If you want to call several APIs, acquire a token for each resource, each time calling AcquireTokenForClient. MSAL uses the application token cache to avoid unnecessary service calls.

Next steps