services	platforms	author
active-directory	dotnet	dstrockis

Calling a downstream web API from a web API using Azure AD

In this sample, native client calls a web API and then the web API calls another downstream web API after obtaining a token to act On Behalf Of the original user. The sample uses the Active Directory Authentication Library (ADAL) in the native client to obtain a token for the user to call the first web API, and also in the first web API to get a token to act on behalf of the user to call the second web API. Both flows use the OAuth 2.0 protocol to obtain the tokens.

For more information about how the protocols work in this scenario and other scenarios, see Authentication Scenarios for Azure AD.

Looking for previous versions of this code sample? Check out the tags on the releases GitHub page.

How To Run This Sample

To run this sample you will need:

Visual Studio 2013
An Internet connection
An Azure Active Directory (Azure AD) tenant. For more information on how to get an Azure AD tenant, please see How to get an Azure AD tenant
A user account in your Azure AD tenant. This sample will not work with a Microsoft account, so 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-webapi-onbehalfof.git

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

There are two projects in this sample. Each needs to be separately registered in your Azure AD tenant.

Register the TodoListService web API

Sign in to the Azure portal.
On the top bar, click on your account and under the Directory list, choose the Active Directory tenant where you wish to register your application.
Click on More Services in the left hand nav, and choose Azure Active Directory.
Click on App registrations and choose Add.
Enter a friendly name for the application, for example 'TodoListService' and select 'Web Application and/or Web API' as the Application Type. For the sign-on URL, enter the base URL for the sample, which is by default https://localhost:44321. For the App ID URI, enter https://<your_tenant_name>/TodoListService, replacing <your_tenant_name> with the name of your Azure AD tenant. Click on Create to create the application.
While still in the Azure portal, choose your application, click on Settings and choose Properties.
Find the Application ID value and copy it to the clipboard.
From the Settings menu, choose Keys and add a key - select a key duration of either 1 year or 2 years. When you save this page, the key value will be displayed, copy and save the value in a safe location - you will 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 please record it as soon as it is visible from the Azure Portal.

NOTE: In this sample, the TodoListService makes a delegated identity call to the Graph API to read the user's profile. By default, when the TodoListService is registered with Active Directory, it is configured to request this permission in the "Required Permissions" configuration section. If you modify the TodoListService to call a different API, or if you build your own service that makes an On Behalf Of call, the service it calls and the permissions it requires must be added to the "Required Permissions" configuration in Azure AD.

Register the TodoListClient app

Sign in to the Azure portal.
On the top bar, click on your account and under the Directory list, choose the Active Directory tenant where you wish to register your application.
Click on More Services in the left hand nav, and choose Azure Active Directory.
Click on App registrations and choose Add.
Enter a friendly name for the application, for example 'TodoListClient-DotNet' and select 'Native' as the Application Type. For the redirect URI, enter https://TodoListClient. Please note that the Redirect URI will not be used in this sample, but it needs to be defined nonetheless. Click on Create to create the application.
While still in the Azure portal, choose your application, click on Settings and choose Properties.
Find the Application ID value and copy it to the clipboard.
Configure Permissions for your application - in the Settings menu, choose the 'Required permissions' section, click on Add, then Select an API, and type 'TodoListService' in the textbox. Then, click on Select Permissions and select 'Access TodoListService'.

Configure known client applications

For the middle tier web API to be able to call the downstream web API, the user must grant the middle tier permission to do so in the form of consent. Because the middle tier has no interactive UI of its own, you need to explicitly bind the client app registration in Azure AD with the registration for the web API, which merges the consent required by both the client & middle tier into a single dialog. You can do so by adding the "Client ID" of the client app, to the manifest of the web API in the knownClientApplications property. Here's how:

Navigate to your 'TodoListService' app registration, and open the manifest editor.
In the manifest, locate the knownClientApplications array property, and add the Client ID of your client application as an element. Your code should look like the following after you're done: "knownClientApplications": ["94da0930-763f-45c7-8d26-04d5938baab2"]
Save the TodoListService manifest by clicking the "Save" button.

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

Configure the TodoListService project

Open the solution in Visual Studio 2013.
Open the web.config file.
Find the app key ida:Tenant and replace the value with your AAD tenant name.
Find the app key ida:Audience and replace the value with the App ID URI you registered earlier, for example https://<your_tenant_name>/TodoListService.
Find the app key ida:ClientId and replace the value with the Client ID for the TodoListService from the Azure portal.
Find the app key ida:AppKey and replace the value with the key for the TodoListService from the Azure portal.

Configure the TodoListClient project

Open `app.config'.
Find the app key ida:Tenant and replace the value with your AAD tenant name.
Find the app key ida:ClientId and replace the value with the Client ID for the TodoListClient from the Azure portal.
Find the app key ida:RedirectUri and replace the value with the Redirect URI for the TodoListClient from the Azure portal, for example http://TodoListClient.
Find the app key todo:TodoListResourceId and replace the value with the App ID URI of the TodoListService, for example https://<your_tenant_name>/TodoListService
Find the app key todo:TodoListBaseAddress and replace the value with the base address of the TodoListService project.

Step 4: Trust the IIS Express SSL certificate

Since the web API is SSL protected, the client of the API (the web app) will refuse the SSL connection to the web API unless it trusts the API's SSL certificate. Use the following steps in Windows Powershell to trust the IIS Express SSL certificate. You only need to do this once. If you fail to do this step, calls to the TodoListService will always throw an unhandled exception where the inner exception message is:

"The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel."

To configure your computer to trust the IIS Express SSL certificate, begin by opening a Windows Powershell command window as Administrator.

Query your personal certificate store to find the thumbprint of the certificate for CN=localhost:

PS C:\windows\system32> dir Cert:\LocalMachine\My


    Directory: Microsoft.PowerShell.Security\Certificate::LocalMachine\My


Thumbprint                                Subject
----------                                -------
C24798908DA71693C1053F42A462327543B38042  CN=localhost

Next, add the certificate to the Trusted Root store:

PS C:\windows\system32> $cert = (get-item cert:\LocalMachine\My\C24798908DA71693C1053F42A462327543B38042)
PS C:\windows\system32> $store = (get-item cert:\Localmachine\Root)
PS C:\windows\system32> $store.Open("ReadWrite")
PS C:\windows\system32> $store.Add($cert)
PS C:\windows\system32> $store.Close()

You can verify the certificate is in the Trusted Root store by running this command:

PS C:\windows\system32> dir Cert:\LocalMachine\Root

Step 5: 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.

Explore the sample by signing in, adding items to the To Do list, removing the user account, and starting again. The To Do list service will take the user's access token, received from the client, and use it to get another access token so it can act On Behalf Of the user in the Graph API. This sample does not cache the user's access token at the To Do list service, so it requests a new access token on every request. The service could cache the access token in a database, for example, for better performance, and it could cache the refresh token so that it could obtain access tokens for the user even when the user is not present.

How To Deploy This Sample to Azure

Coming soon.

About The Code