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A web app that calls web APIs: Call a web API

  • Artikkeli

Now that you have a token, you can call a protected web API. You usually call a downstream API from the controller or pages of your web app.

Call a protected web API

Calling a protected web API depends on your language and framework of choice:

When you use Microsoft.Identity.Web, you have three usage options for calling an API:

Option 1: Call Microsoft Graph with the SDK

In this scenario, you call Microsoft Graph by adding the Microsoft.Identity.Web.GraphServiceClient NuGet package and including .AddMicrosoftGraph() in Startup.cs as specified in Code configuration. You can then directly inject the GraphServiceClient into your controller or page constructor to use it in the actions. The following example Razor page displays the photo of the signed-in user.

[Authorize]
[AuthorizeForScopes(Scopes = new[] { "user.read" })]
public class IndexModel : PageModel
{
 private readonly GraphServiceClient _graphServiceClient;

 public IndexModel(GraphServiceClient graphServiceClient)
 {
    _graphServiceClient = graphServiceClient;
 }

 public async Task OnGet()
 {
  var user = await _graphServiceClient.Me.GetAsync();
  try
  {
   using (var photoStream = await _graphServiceClient.Me.Photo.Content.GetAsync())
   {
    byte[] photoByte = ((MemoryStream)photoStream).ToArray();
    ViewData["photo"] = Convert.ToBase64String(photoByte);
   }
   ViewData["name"] = user.DisplayName;
  }
  catch (Exception)
  {
   ViewData["photo"] = null;
  }
 }
}

For a full sample, see ASP.NET Core web app that calls Microsoft Graph.

Option 2: Call a downstream web API with the helper class

You want to call a web API other than Microsoft Graph. In that case, you add AddDownstreamApi in Startup.cs as specified in Code configuration, and you can directly inject an IDownstreamApi service in your controller or page constructor and use it in the actions:

[Authorize]
[AuthorizeForScopes(ScopeKeySection = "TodoList:Scopes")]
public class TodoListController : Controller
{
  private IDownstreamApi _downstreamApi;
  private const string ServiceName = "TodoList";

  public TodoListController(IDownstreamApi downstreamApi)
  {
    _downstreamApi = downstreamApi;
  }

  public async Task<ActionResult> Details(int id)
  {
    var value = await _downstreamApi.CallApiForUserAsync(
      ServiceName,
      options =>
      {
        options.RelativePath = $"me";
      });
      return View(value);
  }
}

The CallWebApiForUserAsync also has strongly typed generic overrides that enable you to directly receive an object. For example, the following method receives a Todo instance, which is a strongly typed representation of the JSON returned by the web API.

    // GET: TodoList/Details/5
    public async Task<ActionResult> Details(int id)
    {
        var value = await _downstreamApi.CallApiForUserAsync<object, Todo>(
            ServiceName,
            null,
            options =>
            {
                options.HttpMethod = HttpMethod.Get;
                options.RelativePath = $"api/todolist/{id}";
            });
        return View(value);
    }

For a full sample, see ASP.NET Core web app that calls an API

Option 3: Call a downstream web API without the helper class

You've decided to acquire a token manually using the IAuthorizationHeaderProvider service, and you now need to use the token. In that case, the following code continues the example code shown in A web app that calls web APIs: Acquire a token for the app. The code is called in the actions of the web app controllers.

After you've acquired the token, use it as a bearer token to call the downstream API, in this case Microsoft Graph.

public async Task<IActionResult> Profile()
{
  // Acquire the access token.
  string[] scopes = new string[]{"user.read"};
  string authorizationHeader = await IAuthorizationHeaderProvider.GetAuthorizationHeaderForUserAsync(scopes);

  // Use the access token to call a protected web API.
  HttpClient httpClient = new HttpClient();
  client.DefaultRequestHeaders.Add("Authorization", authorizationHeader);

  var response = await httpClient.GetAsync($"{webOptions.GraphApiUrl}/beta/me");

  if (response.StatusCode == HttpStatusCode.OK)
  {
    var content = await response.Content.ReadAsStringAsync();

    dynamic me = JsonConvert.DeserializeObject(content);
    ViewData["Me"] = me;
  }

  return View();
}

Note

You can use the same principle to call any web API.

Most Azure web APIs provide an SDK that simplifies calling the API as is the case for Microsoft Graph.

Next steps

  • Learn more by building an ASP.NET Core web app that signs in users in the following multi-part tutorial series

  • Explore Microsoft identity platform web app samples