Saturday, August 24, 2019

Calling a Web API in a daemon app or long-running process

Overview

This sample demonstrates a Desktop daemon application calling a ASP.NET Web API that is secured using Azure Active Directory. This scenario is useful for situations where a headless, or unattended job, or process, needs to run as an application identity, instead of as a user's identity.
  1. The .Net TodoListDaemon application uses the Active Directory Authentication Library (ADAL) to obtain a JWT access token from Azure Active Directory (Azure AD). The token is requested using the OAuth 2.0 Client Credentials flow, where the client credential is a password. You could also use a certificate to prove the identity of the app. Client credential with certificate is the object of another sample: active-directory-dotnet-daemon-certificate-credential sample.
  2. The access token is used as a bearer token to authenticate the user when calling the TodoListService ASP.NET Web API.

Scenario

Once the service started, when you start the TodoListDaemon desktop application, it repeatedly:
  • adds items to the todo list maintained by the service
  • lists the existing items.
No user interaction is involved.

How to run this sample

To run this sample, you'll need:
  • Visual Studio 2017
  • An Internet connection
  • An Azure Active Directory (Azure AD) tenant. For more information on how to get an Azure AD tenant, see How to get an Azure AD tenant
  • A user account that is an global admin of your Azure AD tenant. This sample will not work with a Microsoft account (formerly Windows Live account). Therefore, if you signed in to the Azure portal with a Microsoft account and have never created a user account in your directory before, you need to do that now.

Step 1: Clone or download this repository

From your shell or command line:
git clone https://github.com/Azure-Samples/active-directory-dotnet-daemon.git
Given that the name of the sample is pretty long, and so are the name of the referenced NuGet pacakges, you might want to clone it in a folder close to the root of your hard drive, to avoid file size limitations on Windows.

Step 2: Register the sample application with your Azure Active Directory tenant

There are two projects in this sample. Each needs to be separately registered in your Azure AD tenant. To register these projects, you can:
If you want to use this automation, read the instructions in App Creation Scripts

Choose the Azure AD tenant where you want to create your applications

As a first step you'll need to:
  1. Sign in to the Azure portal using either a work or school account or a personal Microsoft account.
  2. If your account gives you access to more than one tenant, select your account in the top right corner, and set your portal session to the desired Azure AD tenant (using Switch Directory).
  3. In the left-hand navigation pane, select the Azure Active Directory service, and then select App registrations (Preview).

Register the service app (todoListService_web_daemon_v1)

  1. In App registrations page, select New registration.
  2. When the Register an application page appears, enter your application's registration information:
    • In the Name section, enter a meaningful application name that will be displayed to users of the app, for example todoListService_web_daemon_v1.
    • In the Supported account types section, select Accounts in this organizational directory only ({tenant name}).
  3. Select Register to create the application.
  4. On the app Overview page, find the Application (client) ID value and record it for later. You'll need it to configure the Visual Studio configuration file for this project.
  5. In the list of pages for the app, select on Expose an API
    • For Application ID URI, set it to https://<your_tenant_name>/todoListService_web_daemon_v1 and pres Save

Step 2: Secure your Web API by defining Application Roles (permission)

If you don't do anything more, Azure AD will provide a token for any daemon application (using the client credential flow) requesting an access token for your Web API (for its App ID URI) In this step we are going to ensure that Azure AD only provides a token to the applications to which the Tenant admin grants consent. We are going to limit the access to our TodoList client by defining authorizations
Add an app role to the manifest
  1. While still in the blade for your application, click Manifest.
  2. Edit the manifest by locating the appRoles setting and adding an application roles. The role definition is provided in the JSON block below. Leave the allowedMemberTypes to "Application" only.
  3. Save the manifest.
The content of appRoles should be the following (the id can be any unique GUID)
"appRoles": [
    {
    "allowedMemberTypes": [ "Application" ],
    "description": "Accesses the todoListService_web_daemon_v1 as an application.",
    "displayName": "access_as_application",
    "id": "ccf784a6-fd0c-45f2-9c08-2f9d162a0628",
    "isEnabled": true,
    "lang": null,
    "origin": "Application",
    "value": "access_as_application"
    }
],
Ensure that tokens Azure AD issues tokens for your Web API only to allowed clients
The Web API tests for the app role (that's the developer way of doing it). But you can even ask Azure Active Directory to issue a token for your Web API only to applications which were approved by the tenant admin. For this:
  1. On the app Overview page for your app registration, select the hyperlink with the name of your application in Managed application in local directory (note this field title can be truncated for instance Managed application in ...)
When you select this link you will navigate to the Enterprise Application Overview page associated with the service principal for your application in the tenant where you created it. You can navigate back to the app registration page by using the back button of your browser.
  1. Select the Properties page in the Manage section of the Enterprise application pages
  2. If you want AAD to enforce access to your Web API from only certain clients, set User assignment required? to Yes.
Important security tip
By setting User assignment required? to Yes, AAD will check the app role assignments of the clients when they request an access token for the Web API (see app permissions below). If the client was not be assigned to any AppRoles, AAD would just return invalid_client: AADSTS501051: Application xxxx is not assigned to a role for the xxxx
If you keep User assignment required? to No, Azure AD won’t check the app role assignments when a client requests an access token to your Web API. Therefore, any daemon client (that is any client using client credentials flow) would be able to obtain the access token for the Web API just by specifying its audience (App ID URi). Now, there is a second level of security as your Web API can, as is done in this sample, verify that the application has the right role (which was authorized by the tenant admin). It does it by validating that the access token has a roles claim, and that this claims contains access_as_application.
  1. Select Save

Register the client app (todoList_web_daemon_v1)

  1. In App registrations page, select New registration.
  2. When the Register an application page appears, enter your application's registration information:
    • In the Name section, enter a meaningful application name that will be displayed to users of the app, for example todoList_web_daemon_v1.
    • In the Supported account types section, Accounts in this organizational directory only ({tenant name}).
  3. Select Register to create the application.
  4. On the app Overview page, find the Application (client) ID value and record it for later. You'll need it to configure the Visual Studio configuration file for this project.
  5. From the Certificates & secrets page, in the Client secrets section, choose New client secret:
    • Type a key description (of instance app secret),
    • Select a key duration of either In 1 year, In 2 years, or Never Expires.
    • When you press the Add button, the key value will be displayed, copy, and save the value in a safe location.
    • You'll need this key later to configure the project in Visual Studio. This key value will not be displayed again, nor retrievable by any other means, so record it as soon as it is visible from the Azure portal.
  6. In the list of pages for the app, select API permissions
    • Click the Add a permission button and then,
    • Ensure that the My APIs tab is selected
    • In the list of APIs, select the API todoListService_web_daemon_v1
      • In the Application Permissions section, ensure that the right permissions are checked: access_as_application'. Use the search box if necessary.
      • Select the Add permissions button
  7. You can remove the default permission User.Read as our client is a daemon app. there is no user.
  8. At this stage permissions are assigned correctly. However, by definition, daemon applications does not allow interaction. Therefore no consent can be presented via a UI and accepted to use the service app. The tenant admin need to consent for the client to access your application. for this Click the Grant/revoke admin consent for {tenant} button, and then select Yes when you are asked if you want to grant consent for the requested permissions for all account in the tenant. You need to be an Azure AD tenant admin to do this.

Step 3: Configure the sample to use your Azure AD tenant

In the steps below, "ClientID" is the same as "Application ID" or "AppId".
Open the solution in Visual Studio to configure the projects

Configure the service project

Note: if you used the setup scripts, the changes below will have been applied for you
  1. Open the TodoListService\Web.Config file
  2. Find the app key ida:Tenant and replace the existing value with your Azure AD tenant name.
  3. Find the app key ida:Audience and replace the existing value with the App ID URI you registered earlier for the todoListService_web_daemon_v1 app. For instance use https://<your_tenant_name>/todoListService_web_daemon_v1, where <your_tenant_name> is the name of your Azure AD tenant.

Configure the client project

Note: if you used the setup scripts, the changes below will have been applied for you
  1. Open the TodoListDaemon\App.Config file
  2. Find the app key ida:Tenant and replace the existing value with your Azure AD tenant name.
  3. Find the app key ida:ClientId and replace the existing value with the application ID (clientId) of the todoList_web_daemon_v1 application copied from the Azure portal.
  4. Find the app key ida:AppKey and replace the existing value with the key you saved during the creation of the todoList_web_daemon_v1 app, in the Azure portal.
  5. Find the app key todo:TodoListResourceId and replace the existing value with the App ID URI you registered earlier for the todoListService_web_daemon_v1 app. For instance use https://<your_tenant_name>/todoListService_web_daemon_v1, where <your_tenant_name> is the name of your Azure AD tenant.
  6. Find the app key todo:TodoListBaseAddress and replace the existing value with the base address of the todoListService_web_daemon_v1 project (by default https://localhost:44321/).
NOTE: The TodoListService's ida:Audience and TodoListDaemon's todo:TodoListResourceId app key values must not only match the App ID URI you configured, but they must also match each other exactly. This mach includes casing. Otherwise calls to the TodoListService /api/todolist endpoint will fail with "Error: unauthorized".

Step 4: Run the sample

Clean the solution, rebuild the solution, and run it. You might want to go into the solution properties and set both projects as startup projects, with the service project starting first.
See the scenario section above to understand how to run the sample

How to deploy this sample to Azure

This project has one WebApp / Web API projects. To deploy them to Azure Web Sites, you'll need, for each one, to:
  • create an Azure Web Site
  • publish the Web App / Web APIs to the web site, and
  • update its client(s) to call the web site instead of IIS Express.

Create and Publish the TodoListService to an Azure Web Site

  1. Sign in to the Azure portal.
  2. Click Create a resource in the top left-hand corner, select Web + Mobile --> Web App, select the hosting plan and region, and give your web site a name, for example, TodoListService-contoso.azurewebsites.net. Click Create Web Site.
  3. Once the web site is created, click on it to manage it. For this set of steps, download the publish profile by clicking Get publish profile and save it. Other deployment mechanisms, such as from source control, can also be used.
  4. Switch to Visual Studio and go to the TodoListService project. Right click on the project in the Solution Explorer and select Publish. Click Import Profile on the bottom bar, and import the publish profile that you downloaded earlier.
  5. Click on Settings and in the Connection tab, update the Destination URL so that it is https, for example https://TodoListService-contoso.azurewebsites.net. Click Next.
  6. On the Settings tab, make sure Enable Organizational Authentication is NOT selected. Click Save. Click on Publish on the main screen.
  7. Visual Studio will publish the project and automatically open a browser to the URL of the project. If you see the default web page of the project, the publication was successful.

Update the Active Directory tenant application registration for TodoListService

  1. Navigate to the Azure portal.
  2. On the top bar, click on your account and under the Directory list, choose the Active Directory tenant containing the TodoListService application.
  3. On the applications tab, select the TodoListService application.
  4. From the Settings -> Reply URLs menu, update the Sign-On URL, and Reply URL fields to the address of your service, for example https://TodoListService-contoso.azurewebsites.net. Save the configuration.

Update the TodoListDaemon to call the TodoListService Running in Azure Web Sites

  1. In Visual Studio, go to the TodoListDaemon project.
  2. Open TodoListDaemon\App.Config. Only one change is needed - update the todo:TodoListBaseAddress key value to be the address of the website you published, for example, https://TodoListService-contoso.azurewebsites.net.
  3. Run the client! If you are trying multiple different client types (for example, .Net, Windows Store, Android, iOS) you can have them all call this one published web API.
NOTE: Remember, the To Do list is stored in memory in this TodoListService sample. Azure Web Sites will spin down your web site if it is inactive, and your To Do list will get emptied. Also, if you increase the instance count of the web site, requests will be distributed among the instances. To Do will, therefore, not be the same on each instance.

About The Code

Client side: the daemon app

The code acquiring a token is located entirely in the TodoListDaemon\Program.cs file. The Authentication context is created (line 68)
authContext = new AuthenticationContext(authority);
Then a ClientCredential is instantiated (line 69), from the TodoListDaemon application's Client ID and the application secret (appKey).
clientCredential = new ClientCredential(clientId, appKey);
This instance of ClientCredential is used in the PostTodo() and GetTodo() methods as an argument to AcquireTokenAsync to get a token for the Web API (line 96 and 162)
result = await authContext.AcquireTokenAsync(todoListResourceId, clientCredential);
This token is then used as a bearer token to call the Web API (line 127 and 193)
httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", result.AccessToken)

Service side: how the protected API

On the service side, the code directing ASP.NET to validate the access token is in App_Start\Startup.Auth.cs. It only validates the audience of the application (the App ID URI)
 public partial class Startup
 {
  // For more information on configuring authentication, please visit http://go.microsoft.com/fwlink/?LinkId=301864
  public void ConfigureAuth(IAppBuilder app)
  {
   app.UseWindowsAzureActiveDirectoryBearerAuthentication(
      new WindowsAzureActiveDirectoryBearerAuthenticationOptions
      {
       Tenant = ConfigurationManager.AppSettings["ida:Tenant"],
       TokenValidationParameters = new TokenValidationParameters
       {
        ValidAudience = ConfigurationManager.AppSettings["ida:Audience"]
       }
      });
   }
}
However, the controllers also validate that the client has a roles claim of value access_as_application. It returns an Unauthorized error otherwise.
 public IEnumerable<TodoItem> Get()
 {
  //
  // The roles claim tells what permissions the client application has in the service.
  // In this case we look for a roles value of access_as_application
  //
  Claim scopeClaim = ClaimsPrincipal.Current.FindFirst("roles");
  if (scopeClaim == null || (scopeClaim.Value != "access_as_application"))
  {
   throw new HttpResponseException(new HttpResponseMessage { StatusCode = HttpStatusCode.Unauthorized,
      ReasonPhrase = "The 'roles' claim does not contain 'access_as_application'or was not found" });
  }
  ...
 }

How to recreate this sample

First, in Visual Studio create an empty solution to host the projects. Then, follow the following steps to create each project.

Creating the TodoListService Project

  1. In the solution, create a new ASP.Net MVC web API project called TodoListService and while creating the project:
    • Click the Change Authentication button,
    • Select Organizational Accounts, Cloud - Single Organization,
    • Enter the name of your Azure AD tenant,
    • and set the Access Level to Single Sign On. You will be prompted to sign in to your Azure AD tenant.
    NOTE: You must sign in with a user that is in the tenant; you cannot, during this step, sign in with a Microsoft account.
  2. In the folder, add a new class called TodoItem.cs. Copy the implementation of TodoItem from this sample into the class.
  3. Add a new, empty, Web API 2 controller called TodoListController.
  4. Copy the implementation of the TodoListController from this sample into the controller. Don't forget to add the [Authorize] attribute to the class.
  5. In TodoListController resolving missing references by adding using statements for System.Collections.Concurrent, TodoListService.Models, System.Security.Claims.

Creating the TodoListDaemon Project

  1. In the solution, create a new Windows --> Console Application called TodoListDaemon.
  2. Add the (stable) Active Directory Authentication Library (ADAL) NuGet, Microsoft.IdentityModel.Clients.ActiveDirectory, version 1.0.3 (or higher) to the project.
  3. Add assembly references to System.Net.Http, System.Web.Extensions, and System.Configuration.
  4. Add a new class to the project called TodoItem.cs. Copy the code from the sample project file of the same name into this class, completely replacing the code in the new file.
  5. Copy the code from Program.cs in the sample project into the file of the same name in the new project, completely replacing the code in the new file.
  6. In app.config create keys for ida:AADInstance, ida:Tenant, ida:ClientId, ida:AppKey, todo:TodoListResourceId, and todo:TodoListBaseAddress and set them accordingly. For the global Azure cloud, the value of ida:AADInstance is https://login.windows.net/{0}.
Finally, in the properties of the solution itself, set both projects as startup projects.
at

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