Scenario: Web App (Server App) calling Web API

Applies to: Windows Server 2022, Windows Server 2019, AD FS 2019 and later

Learn how to build a web app signing-in users authenticated by AD FS 2019 and acquiring tokens using MSAL library to call web APIs.

Before reading this article, you should be familiar with the AD FS concepts and Authorization code grant flow

Overview

In this flow you add authentication to your Web App (Server App), which can therefore sign in users and calls a web API. From the Web App, to call the Web API, use MSAL's AcquireTokenByAuthorizationCode token acquisition method. You'll use the Authorization code flow, storing the acquired token in the token cache. Then the controller will acquire tokens silently from the cache when needed. MSAL refreshes the token if needed.

Web Apps that calls Web APIs:

• are confidential client applications.
• that's why they've registered a secret (application shared secret, certificate or AD account) with AD FS. This secret is passed-in during the call to AD FS to get a token.

To better understand how to register a Web App in AD FS and to configure it to acquire tokens to call a Web API, let's use a sample available here and walkthrough the app registration and code configuration steps.

Pre-requisites

• GitHub client tools
• AD FS 2019 or later configured and running
• Visual Studio 2013 or later

App Registration in AD FS

This section shows how to register the Web App as a confidential client and Web API as a Relying Party (RP) in AD FS.

1. In AD FS Management, right-click on Application Groups and select Add Application Group.

2. On the Application Group Wizard, for the Name enter WebAppToWebApi and under Client-Server applications select the Server application accessing a Web API template. Click Next.

   

3. Copy the Client Identifier value. It will be used later as the value for ida:ClientId in the applications Web.config file. Enter the following for Redirect URI: - https://localhost:44326. Click Add. Click Next.

   

4. On the Configure Application Credentials screen, place a check in Generate a shared secret and copy the secret. This will be used later as the value for ida:ClientSecret in the applications Web.config file. Click Next.

   

5. On the Configure Web API screen, enter the Identifier: https://webapi. Click Add. Click Next. This value will be used later for ida:GraphResourceId in the applications Web.config file.

   

6. On the Apply Access Control Policy screen, select Permit everyone and click Next.

   

7. On the Configure Application Permissions screen, make sure openid and user_impersonation are selected and click Next.

   

8. On the Summary screen, click Next.

9. On the Complete screen, click Close.

Code Configuration

This section shows how to configure a ASP.NET Web App to sign-in user and retrieve token to call the Web API

1. Download the sample from here

2. Open the sample using Visual Studio

3. Open the web.config file. Modify the following:

   • ida:ClientId - enter the Client Identifier value from #3 in App Registration in AD FS section above.

   • ida:ClientSecret - enter the Secret value from #4 in App Registration in AD FS section above.

   • ida:RedirectUri - enter the Redirect URI value from #3 in App Registration in AD FS section above.

   • ida:Authority - enter https://[your AD FS hostname]/adfs. E.g., https://adfs.contoso.com/adfs

   • ida:Resource - enter the Identifier value from #5 in App Registration in AD FS section above.

     

Test the sample

This section shows how to test the sample configured above.

1. Once the code changes are made rebuild the solution

2. At the top of Visual Studio, make sure Internet Explorer is selected and click the green arrow.

   

3. On Home Page, click on Sign-in.

   

4. You will be re-directed to the AD FS sign-in page. Go ahead and sign in.

   

5. Once signed-in, click on Access Token.

   

6. Clicking on Access Token will get the access token info by calling the Web API

   

Next Steps

AD FS OpenID Connect/OAuth flows and Application Scenarios